[core] Encapsulate split serialization protocols

[leaves12138]

What

• Keep SplitSerializer focused on the outer frame, stable type ids, and type dispatch.
• Move IncrementalSplit binary serialization into public serialize(DataOutputView) and deserialize(DataInputView) methods, matching DataSplit, ChainSplit, and IndexedSplit.
• Let FallbackSplitImpl own its inner isFallback + wrapped split protocol.
• Let QueryAuthSplit own its wrapped split and authorization-result protocol.
• Keep Java writeObject / readObject on the complete outer frame for wrapper splits, avoiding recursive delegation while preserving their Java serialization layout.

Why

SplitSerializer previously duplicated the field-level formats of several split implementations. Wrapper splits also delegated their own serialize methods back to SplitSerializer, which then called split-specific helper methods.

Giving each split ownership of its inner protocol removes the circular delegation and keeps format evolution next to the corresponding data structure. SplitSerializer now only frames and dispatches split types.

Compatibility

• SplitSerializer.VERSION remains 1.
• IncrementalSplit.VERSION remains 1.
• The Java serialization body of IncrementalSplit is unchanged; its existing logic is extracted into reusable methods.
• Wrapper Java serialization continues to use the complete SplitSerializer frame.
• The outer Fallback and QueryAuth split bytes are unchanged.
• split-v1-incremental is refreshed because the outer protocol now delegates to the versioned inner IncrementalSplit payload.

Scope

This PR contains only the split serialization refactor. It does not include DataFileMeta schema or column sequence changes from #9313.

Tests

• SplitSerializerTest
• QueryAuthSplitTest
• Flink PendingSplitsCheckpointSerializerTest
• Core Spotless and Checkstyle

[JingsongLi]

+1