tidy(config): use dataclass for MigrationEntry

The only pydantic usage was to convert strings to `Version` objects. The reason to do this conversion was to allow the register decorator to accept strings. MigrationEntry is only created inside this class, so we can just create versions from each migration when instantiating MigrationEntry instead.

Also, pydantic doesn't provide runtime time checking for arbitrary classes like Version, so we don't get any real benefit.

invokeai/app/services/config/config_migrate.py

@@ -4,31 +4,22 @@
 Utility class for migrating among versions of the InvokeAI app config schema.
 """
 
+from dataclasses import dataclass
 from typing import Any, Callable, List, TypeAlias
 
 from packaging.version import Version
-from pydantic import BaseModel, ConfigDict, field_validator
 
 AppConfigDict: TypeAlias = dict[str, Any]
 
 
-class MigrationEntry(BaseModel):
+@dataclass
+class MigrationEntry:
     """Defines an individual migration."""
 
-    model_config = ConfigDict(arbitrary_types_allowed=True)
-
     from_version: Version
     to_version: Version
     function: Callable[[AppConfigDict], AppConfigDict]
 
-    @field_validator("from_version", "to_version", mode="before")
-    @classmethod
-    def _string_to_version(cls, v: str | Version) -> Version:  # noqa D102
-        if isinstance(v, str):
-            return Version(v)
-        else:
-            return v
-
 
 class ConfigMigrator:
     """This class allows migrators to register their input and output versions."""
@@ -38,8 +29,8 @@ class ConfigMigrator:
     @classmethod
     def register(
         cls,
-        from_version: Version | str,
-        to_version: Version | str,
+        from_version: str,
+        to_version: str,
     ) -> Callable[[Callable[[AppConfigDict], AppConfigDict]], Callable[[AppConfigDict], AppConfigDict]]:
         """Define a decorator which registers the migration between two versions."""
 
@@ -48,7 +39,9 @@ class ConfigMigrator:
                 raise ValueError(
                     f"function {function.__name__} is trying to register a migration for version {str(from_version)}, but this migration has already been registered."
                 )
-            cls._migrations.append(MigrationEntry(from_version=from_version, to_version=to_version, function=function))
+            cls._migrations.append(
+                MigrationEntry(from_version=Version(from_version), to_version=Version(to_version), function=function)
+            )
             return function
 
         return decorator