refactor: migrate stats module to Pydantic

Models converted (8 files, 80+ classes):

stats.py (base classes):
- Stat, Split, PitchArsenalSplit, ExpectedStatistics, Sabermetrics
- ZoneCodes, Zones, HotColdZones, Chart, SprayCharts
- PitchArsenal, OutsAboveAverage, PlayerGameLogStat

hitting.py:
- SimpleHittingSplit, AdvancedHittingSplit, HittingPlay
- HittingWinLoss, HittingHomeAndAway, HittingCareer, HittingSeason
- HittingGameLog, HittingPlayLog, HittingPitchLog, HittingByMonth
- HittingVsTeam, HittingVsPlayer, HittingExpectedStatistics, etc.

pitching.py:
- SimplePitchingSplit, AdvancedPitchingSplit, PitchingPlay
- PitchingSeason, PitchingCareer, PitchingGameLog, PitchingLog
- PitchingByMonth, PitchingHomeAndAway, PitchingWinLoss
- PitchingVsTeam, PitchingVsPlayer, PitchingRankings, etc.

fielding.py:
- SimpleFieldingSplit, FieldingSeason, FieldingCareer
- FieldingHomeAndAway, FieldingGameLog, FieldingByMonth, etc.

catching.py:
- SimpleCatchingSplit, CatchingSeason, CatchingCareer
- CatchingGameLog, CatchingHomeAndAway, CatchingWinLoss, etc.

running.py:
- RunningOpponentsFaced

game.py:
- SimpleGameStats, SeasonGame, CareerGame
- CareerRegularSeasonGame, CareerPlayoffsGame

Key changes:
- All fields use snake_case with aliases for API compatibility
- Fixed type mismatches: stolenbasepercentage, groundoutstoairouts,
  atbatsperhomerun, whiffpercentage are strings not ints
- Game model fields made optional for stats endpoint compatibility
- Field validators handle empty dicts from API as None
- Updated all stats tests to use new Pythonic field names
  (totalsplits -> total_splits)

Author: Mattsface

mlbstatsapi/models/game/game.py

@@ -1,3 +1,4 @@
+from typing import Optional
 from pydantic import Field
 from mlbstatsapi.models.base import MLBBaseModel
 from mlbstatsapi.models.game.gamedata import GameData
@@ -24,9 +25,9 @@ class Game(MLBBaseModel):
     """
     game_pk: int = Field(alias="gamepk")
     link: str
-    metadata: MetaData
-    game_data: GameData = Field(alias="gamedata")
-    live_data: LiveData = Field(alias="livedata")
+    metadata: Optional[MetaData] = None
+    game_data: Optional[GameData] = Field(default=None, alias="gamedata")
+    live_data: Optional[LiveData] = Field(default=None, alias="livedata")
 
     @property
     def id(self) -> int: