feat: refactor services folder/module structure

Refactor services folder/module structure.

**Motivation**

While working on our services I've repeatedly encountered circular imports and a general lack of clarity regarding where to put things. The structure introduced goes a long way towards resolving those issues, setting us up for a clean structure going forward.

**Services**

Services are now in their own folder with a few files:

- `services/{service_name}/__init__.py`: init as needed, mostly empty now
- `services/{service_name}/{service_name}_base.py`: the base class for the service
- `services/{service_name}/{service_name}_{impl_type}.py`: the default concrete implementation of the service - typically one of `sqlite`, `default`, or `memory`
- `services/{service_name}/{service_name}_common.py`: any common items - models, exceptions, utilities, etc

Though it's a bit verbose to have the service name both as the folder name and the prefix for files, I found it is _extremely_ confusing to have all of the base classes just be named `base.py`. So, at the cost of some verbosity when importing things, I've included the service name in the filename.

There are some minor logic changes. For example, in `InvocationProcessor`, instead of assigning the model manager service to a variable to be used later in the file, the service is used directly via the `Invoker`.

**Shared**

Things that are used across disparate services are in `services/shared/`:

- `default_graphs.py`: previously in `services/`
- `graphs.py`: previously in `services/`
- `paginatation`: generic pagination models used in a few services
- `sqlite`: the `SqliteDatabase` class, other sqlite-specific things

invokeai/app/services/session_queue/session_queue_base.py

@@ -1,7 +1,6 @@
 from abc import ABC, abstractmethod
 from typing import Optional
 
-from invokeai.app.services.graph import Graph
 from invokeai.app.services.session_queue.session_queue_common import (
     QUEUE_ITEM_STATUS,
     Batch,
@@ -18,6 +17,7 @@ from invokeai.app.services.session_queue.session_queue_common import (
     SessionQueueItemDTO,
     SessionQueueStatus,
 )
+from invokeai.app.services.shared.graph import Graph
 from invokeai.app.services.shared.pagination import CursorPaginatedResults
 
 

invokeai/app/services/session_queue/session_queue_common.py

@@ -7,7 +7,7 @@ from pydantic import BaseModel, Field, StrictStr, parse_raw_as, root_validator,
 from pydantic.json import pydantic_encoder
 
 from invokeai.app.invocations.baseinvocation import BaseInvocation
-from invokeai.app.services.graph import Graph, GraphExecutionState, NodeNotFoundError
+from invokeai.app.services.shared.graph import Graph, GraphExecutionState, NodeNotFoundError
 from invokeai.app.util.misc import uuid_string
 
 # region Errors

invokeai/app/services/session_queue/session_queue_sqlite.py

@@ -5,8 +5,7 @@ from typing import Optional, Union, cast
 from fastapi_events.handlers.local import local_handler
 from fastapi_events.typing import Event as FastAPIEvent
 
-from invokeai.app.services.events import EventServiceBase
-from invokeai.app.services.graph import Graph
+from invokeai.app.services.events.events_base import EventServiceBase
 from invokeai.app.services.invoker import Invoker
 from invokeai.app.services.session_queue.session_queue_base import SessionQueueBase
 from invokeai.app.services.session_queue.session_queue_common import (
@@ -29,8 +28,9 @@ from invokeai.app.services.session_queue.session_queue_common import (
     calc_session_count,
     prepare_values_to_insert,
 )
-from invokeai.app.services.shared.sqlite import SqliteDatabase
+from invokeai.app.services.shared.graph import Graph
 from invokeai.app.services.shared.pagination import CursorPaginatedResults
+from invokeai.app.services.shared.sqlite import SqliteDatabase
 
 
 class SqliteSessionQueue(SessionQueueBase):