Fix physical distinctness expression nullability

[blinding-pixels]

Which issue does this PR close?

• Closes Physical distinctness expressions incorrectly report nullable output #24096

Rationale for this change

When aggregate CSE extracts a repeated truth check, the logical and physical plans assign different nullability metadata to it, causing planning to fail. Since these truth checks always return either true or false, the physical plan should mark them as non-nullable.

What changes are included in this PR?

This PR updates physical BinaryExpr nullability so IS DISTINCT FROM and IS NOT DISTINCT FROM are always reported as non-nullable.

It also adds a focused unit-test matrix and a SQL logic regression covering the aggregate CSE path reported in the issue.

Are these changes tested?

Yes. The tests cover both distinctness operators, ordinary equality as a control, and the reported aggregate query.

Formatting, Clippy, focused tests, and the extended workspace test suite all pass.

Are there any user-facing changes?

Yes. Affected queries using repeated truth checks on nullable Boolean values now plan and execute instead of failing with a logical/physical schema mismatch.

There are no public API changes.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.94737% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.99%. Comparing base (a9b61ab) to head (fac096a).

Files with missing lines	Patch %	Lines
datafusion/physical-expr/src/expressions/binary.rs	78.94%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24244      +/-   ##
==========================================
- Coverage   80.99%   80.99%   -0.01%     
==========================================
  Files        1106     1106              
  Lines      383549   383567      +18     
  Branches   383549   383567      +18     
==========================================
+ Hits       310644   310654      +10     
  Misses      54570    54570              
- Partials    18335    18343       +8     

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