feat(api): chore: pydantic & fastapi upgrade

Upgrade pydantic and fastapi to latest.

- pydantic~=2.4.2
- fastapi~=103.2
- fastapi-events~=0.9.1

**Big Changes**

There are a number of logic changes needed to support pydantic v2. Most changes are very simple, like using the new methods to serialized and deserialize models, but there are a few more complex changes.

**Invocations**

The biggest change relates to invocation creation, instantiation and validation.

Because pydantic v2 moves all validation logic into the rust pydantic-core, we may no longer directly stick our fingers into the validation pie.

Previously, we (ab)used models and fields to allow invocation fields to be optional at instantiation, but required when `invoke()` is called. We directly manipulated the fields and invocation models when calling `invoke()`.

With pydantic v2, this is much more involved. Changes to the python wrapper do not propagate down to the rust validation logic - you have to rebuild the model. This causes problem with concurrent access to the invocation classes and is not a free operation.

This logic has been totally refactored and we do not need to change the model any more. The details are in `baseinvocation.py`, in the `InputField` function and `BaseInvocation.invoke_internal()` method.

In the end, this implementation is cleaner.

**Invocation Fields**

In pydantic v2, you can no longer directly add or remove fields from a model.

Previously, we did this to add the `type` field to invocations.

**Invocation Decorators**

With pydantic v2, we instead use the imperative `create_model()` API to create a new model with the additional field. This is done in `baseinvocation.py` in the `invocation()` wrapper.

A similar technique is used for `invocation_output()`.

**Minor Changes**

There are a number of minor changes around the pydantic v2 models API.

**Protected `model_` Namespace**

All models' pydantic-provided methods and attributes are prefixed with `model_` and this is considered a protected namespace. This causes some conflict, because "model" means something to us, and we have a ton of pydantic models with attributes starting with "model_".

Forunately, there are no direct conflicts. However, in any pydantic model where we define an attribute or method that starts with "model_", we must tell set the protected namespaces to an empty tuple.

```py
class IPAdapterModelField(BaseModel):
    model_name: str = Field(description="Name of the IP-Adapter model")
    base_model: BaseModelType = Field(description="Base model")

    model_config = ConfigDict(protected_namespaces=())
```

**Model Serialization**

Pydantic models no longer have `Model.dict()` or `Model.json()`.

Instead, we use `Model.model_dump()` or `Model.model_dump_json()`.

**Model Deserialization**

Pydantic models no longer have `Model.parse_obj()` or `Model.parse_raw()`, and there are no `parse_raw_as()` or `parse_obj_as()` functions.

Instead, you need to create a `TypeAdapter` object to parse python objects or JSON into a model.

```py
adapter_graph = TypeAdapter(Graph)
deserialized_graph_from_json = adapter_graph.validate_json(graph_json)
deserialized_graph_from_dict = adapter_graph.validate_python(graph_dict)
```

**Field Customisation**

Pydantic `Field`s no longer accept arbitrary args.

Now, you must put all additional arbitrary args in a `json_schema_extra` arg on the field.

**Schema Customisation**

FastAPI and pydantic schema generation now follows the OpenAPI version 3.1 spec.

This necessitates two changes:
- Our schema customization logic has been revised
- Schema parsing to build node templates has been revised

The specific aren't important, but this does present additional surface area for bugs.

**Performance Improvements**

Pydantic v2 is a full rewrite with a rust backend. This offers a substantial performance improvement (pydantic claims 5x to 50x depending on the task). We'll notice this the most during serialization and deserialization of sessions/graphs, which happens very very often - a couple times per node.

I haven't done any benchmarks, but anecdotally, graph execution is much faster. Also, very larges graphs - like with massive iterators - are much, much faster.

invokeai/backend/model_management/model_manager.py

@@ -236,13 +236,13 @@ import types
 from dataclasses import dataclass
 from pathlib import Path
 from shutil import move, rmtree
-from typing import Callable, Dict, List, Literal, Optional, Set, Tuple, Union
+from typing import Callable, Dict, List, Literal, Optional, Set, Tuple, Union, cast
 
 import torch
 import yaml
 from omegaconf import OmegaConf
 from omegaconf.dictconfig import DictConfig
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, ConfigDict, Field
 
 import invokeai.backend.util.logging as logger
 from invokeai.app.services.config import InvokeAIAppConfig
@@ -294,6 +294,8 @@ class AddModelResult(BaseModel):
     base_model: BaseModelType = Field(description="The base model")
     config: ModelConfigBase = Field(description="The configuration of the model")
 
+    model_config = ConfigDict(protected_namespaces=())
+
 
 MAX_CACHE_SIZE = 6.0  # GB
 
@@ -576,7 +578,7 @@ class ModelManager(object):
         """
         model_key = self.create_key(model_name, base_model, model_type)
         if model_key in self.models:
-            return self.models[model_key].dict(exclude_defaults=True)
+            return self.models[model_key].model_dump(exclude_defaults=True)
         else:
             return None  # TODO: None or empty dict on not found
 
@@ -632,7 +634,7 @@ class ModelManager(object):
                 continue
 
             model_dict = dict(
-                **model_config.dict(exclude_defaults=True),
+                **model_config.model_dump(exclude_defaults=True),
                 # OpenAPIModelInfoBase
                 model_name=cur_model_name,
                 base_model=cur_base_model,
@@ -900,14 +902,16 @@ class ModelManager(object):
         Write current configuration out to the indicated file.
         """
         data_to_save = dict()
-        data_to_save["__metadata__"] = self.config_meta.dict()
+        data_to_save["__metadata__"] = self.config_meta.model_dump()
 
         for model_key, model_config in self.models.items():
             model_name, base_model, model_type = self.parse_key(model_key)
             model_class = self._get_implementation(base_model, model_type)
             if model_class.save_to_config:
                 # TODO: or exclude_unset better fits here?
-                data_to_save[model_key] = model_config.dict(exclude_defaults=True, exclude={"error"})
+                data_to_save[model_key] = cast(BaseModel, model_config).model_dump(
+                    exclude_defaults=True, exclude={"error"}, mode="json"
+                )
                 # alias for config file
                 data_to_save[model_key]["format"] = data_to_save[model_key].pop("model_format")