Support dotted field access on struct lambda parameters in SQL exprs

[shehab-ali]

Which issue does this PR close?

• Closes #.

Rationale for this change

Struct-valued lambda parameters cannot currently be accessed using dotted field syntax. For example, the following query fails because record.rule_action is resolved as a table-qualified column instead of field access on the lambda parameter:

SELECT array_transform(
  records,
  record -> record.rule_action
);

What changes are included in this PR?

When a compound identifier begins with an active lambda parameter, resolve the root as a lambda variable and plan each remaining identifier as named struct-field access.
This supports expressions such as:

record.rule_action
record.metadata.rule_action
record.items[1]

Field access is planned through the configured expression planners, consistent with existing field-access handling.

What is the testing strategy for this PR?

Added sqllogictest coverage in array/array_transform.slt for:

• Direct field access on a struct-valued lambda parameter.
• Field access followed by list indexing.
• Chained field access through nested structs.

Are there any user-facing changes?

no

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.90%. Comparing base (5747e87) to head (4e1c42e).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/sql/src/expr/identifier.rs	85.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #25177    +/-   ##
========================================
  Coverage   81.90%   81.90%            
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  Files        1132     1132            
  Lines      420155   420590   +435     
  Branches   420155   420590   +435     
========================================
+ Hits       344126   344499   +373     
- Misses      55742    55771    +29     
- Partials    20287    20320    +33     

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