Refactor schema rewriter: remove lifetimes, extract column/cast helpers, add mismatch coverage

[kosiew]

Which issue does this PR close?

• Closes PhysicalExprAdapter - Schema Rewriter Cleanup #20161.

Rationale for this change

This change is a focused refactor of the PhysicalExprAdapter schema rewriter to improve readability and maintainability while preserving behavior.

Key motivations:

• Reduce complexity from explicit lifetimes by storing schema references as SchemaRef.
• Make column/index/type handling easier to follow by extracting helper functions.
• Strengthen the test suite to ensure refactors do not alter adapter output.

What changes are included in this PR?

• Refactored DefaultPhysicalExprAdapterRewriter to own SchemaRef values instead of borrowing &Schema.

  • Simplifies construction and avoids lifetime plumbing.

• Simplified column rewrite logic by:

  • Early-exiting when both the physical index and data type already match.
  • Extracting resolve_column to handle physical index/name resolution.
  • Extracting create_cast_column_expr to validate cast compatibility (including nested structs) and build CastColumnExpr.

• Minor cleanups in struct compatibility validation and field selection to ensure the cast checks are performed against the actual physical field resolved by the final column index.

• Test updates and additions:

  • Simplified construction of expected struct Fields in tests for clarity.
  • Added test_rewrite_column_index_and_type_mismatch to validate the combined case where the logical column index differs from the physical schema and the data type requires casting.

Are these changes tested?

Yes.

• Existing unit tests continue to pass.

• Added a new unit test to cover the index-and-type mismatch scenario for column rewriting, asserting:

  • The inner Column points to the correct physical index.
  • The resulting expression is a CastColumnExpr producing the expected logical type.

Are there any user-facing changes?

No.

• This is a refactor/cleanup intended to preserve existing behavior.
• No public API changes, no behavioral changes expected in query results.

LLM-generated code disclosure

This PR includes LLM-generated code and comments. All LLM-generated content has been manually reviewed and tested.

[adriangb]

Thanks @kosiew !

[kosiew]

@adriangb
Thanks for the quick review and approval.
Working on #20162 next.