refactor(proto): destructure CASE and IN-list expression serde hooks

[buraksenn]

Which issue does this PR close?

• Closes Destructure proto hooks for CASE and IN-list physical expressions #24616.

Rationale for this change

Proto hooks that access fields individually can silently omit newly added state. Exhaustive destructuring makes such omissions compile errors.

What changes are included in this PR?

• Exhaustively destructure CaseExpr, CaseBody, and InListExpr in their encoders.
• Exhaustively destructure their protobuf nodes in the decoders.
• Document eval_method and static_filter as constructor-derived state.

The behavior and wire format are unchanged.

Are these changes tested?

Covered by the existing CASE and IN-list proto hook tests:

cargo test -p datafusion-physical-expr --features proto case::proto_tests
cargo test -p datafusion-physical-expr --features proto in_list::proto_tests

Are there any user-facing changes?

No.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.29730% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.45%. Comparing base (872df4d) to head (34252d8).

Files with missing lines	Patch %	Lines
datafusion/physical-expr/src/expressions/case.rs	95.65%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24700      +/-   ##
==========================================
- Coverage   81.45%   81.45%   -0.01%     
==========================================
  Files        1119     1119              
  Lines      400411   400428      +17     
  Branches   400411   400428      +17     
==========================================
+ Hits       326144   326149       +5     
- Misses      55195    55202       +7     
- Partials    19072    19077       +5     

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