fix: preserve projection field metadata during physical planning

[subotac]

Which issue does this PR close?

• Closes Missing field metadata for projections during physical planning #23529.

Rationale for this change

Logical projection aliases can attach field metadata, but physical projection planning derived its output schema only from the unwrapped physical expressions. This caused schema validation to reject
aggregates above such projections.

What changes are included in this PR?

• Apply logical projection schema and field metadata when constructing ProjectionExec.
• Preserve the existing physical derivation of field names, types, and nullability.
• Add metadata-aware constructors across the physical-expression and physical-plan crate boundary.
• Cover projections with alias metadata followed by aggregation.

Are these changes tested?

Yes. A focused physical planner regression test reproduces the original schema mismatch and passes with the fix. The relevant core and physical-plan unit suites, targeted all-targets/all-features
clippy, formatting, and diff checks also pass.

Are there any user-facing changes?

Projection field metadata is now preserved in physical plans. Two additive constructor methods support passing projection schema metadata across crate boundaries; no existing API is changed.

[kosiew]

@subotac,

This looks good overall. I have one small suggestion to make the metadata-only behavior of the new constructor more explicit and easier to maintain.

[kosiew]

Could we add a focused unit test for try_new_with_schema_metadata? It would be helpful to assert the exact output schema and field metadata, while also confirming that the expression-derived name, type, and nullability remain unchanged. The planner regression test covers the aggregate failure, but a constructor-level test would document this API's metadata-only contract and test it independently of aggregate validation.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.89655% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.89%. Comparing base (1955d5a) to head (a1d39b0).
⚠️ Report is 59 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/core/src/physical_planner.rs	65.78%	7 Missing and 6 partials ⚠️
datafusion/physical-expr/src/projection.rs	82.35%	5 Missing and 1 partial ⚠️
datafusion/physical-plan/src/projection.rs	95.45%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23981      +/-   ##
==========================================
+ Coverage   80.75%   80.89%   +0.13%     
==========================================
  Files        1096     1102       +6     
  Lines      373582   376228    +2646     
  Branches   373582   376228    +2646     
==========================================
+ Hits       301686   304341    +2655     
+ Misses      53893    53774     -119     
- Partials    18003    18113     +110     

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[subotac]

Added a focused constructor-level test. It uses a metadata schema with deliberately different field name, type, and nullability, then asserts the exact output schema. The expression-derived name, type, and
nullability remain unchanged while field and schema metadata are copied.