refactor(models): Upgrade to pydantic v2

Resolves #4.

backend-flask/models/player_team_availability.py

@@ -47,13 +47,12 @@ class AvailabilitySchema(spec.BaseModel):
             i += 1
 
 class PlayerTeamAvailabilityRoleSchema(spec.BaseModel):
-    from models.player import PlayerSchema
-    from models.player_team_role import RoleSchema
-
-    player: PlayerSchema
+    player: "PlayerSchema"
     playtime: int
     availability: int
-    roles: list[RoleSchema]
+    roles: list["RoleSchema"]
 
 
+from models.player import PlayerSchema
+from models.player_team_role import RoleSchema
 from models.player_team import PlayerTeam

backend-flask/spec.py

@@ -20,8 +20,7 @@ spec = SpecTree(
     nested_naming_strategy=nested_naming_strategy
 )
 
-class BaseModel(pydantic.v1.BaseModel):
+class BaseModel(pydantic.BaseModel):
     class Config:
         alias_generator = to_camel
-        allow_population_by_field_name = True
-        smart_union = True
+        populate_by_name = True