fix: preserve lambda bindings in nested-loop join projection pushdown

[xudong963]

Which issue does this PR close?

• Closes ProjectionPushdown fails on a nested-loop join whose lambda captures a column from the other input #26396.

Rationale for this change

A nested-loop join whose lambda captures a column from the other input can fail during physical optimization with unable to unwrap lambda, even though the query executes correctly with physical optimization disabled.

These queries should work with the default optimizer while retaining projection pushdown for expressions that can be evaluated on one join input.

What changes are included in this PR?

• Keep each lambda and its body in the enclosing high-order function's scope when extracting join-filter expressions. Ordinary sibling expressions, other function arguments, and complete high-order expressions that depend on only one input remain eligible for pushdown.
• Remap captured columns and rebase lambda parameter indices when moving an expression to an input projection, extending the intermediate filter schema, and pruning unused filter columns. Nested lambdas retain their relative parameter offsets and bindings.
• Add nested_loop_join_lambda.slt with result and physical-plan regressions.

This change preserves lambda bodies within their enclosing function; it does not introduce hoisting of individual computations from inside a lambda body.

What is the testing strategy for this PR?

The new SQL test covers the original reproducer with either join-input order, mixed predicates, nested lambdas, parameter shadowing, empty/NULL arrays, and extraction of complete high-order functions onto either input. Different input and filter schema widths exercise parameter rebasing. Three EXPLAIN checks verify that ordinary expressions and complete high-order functions are still pushed down.

Are there any user-facing changes?

Nested-loop joins with lambda predicates now plan and execute with the default physical optimizer. There are no public API or configuration changes.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.95652% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.89%. Comparing base (fe612e2) to head (1349bd7).

Files with missing lines	Patch %	Lines
...sion/physical-optimizer/src/projection_pushdown.rs	86.95%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #26399   +/-   ##
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  Coverage   82.89%   82.89%           
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  Files        1154     1154           
  Lines      458022   458058   +36     
  Branches   458022   458058   +36     
=======================================
+ Hits       379683   379720   +37     
+ Misses      55303    55298    -5     
- Partials    23036    23040    +4     

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[lonless9]

I think this issue is related. #24372

[jayzhan211]

Thanks @xudong963 , LGTM!