polish: reduce function sizes in semantic_function_analysis.f90

[krystophny]

Issue #1929 identified several functions exceeding the 50-line soft limit. PR #1940 addressed the subroutine analysis functions, but the following functions in semantic_function_analysis.f90 still need refactoring:

• determine_function_return_type (67 lines) - line 316
• infer_result_type_from_assignments (51 lines) - line 384
• infer_identifier_type_from_context (61 lines) - line 551
• create_function_scope (70 lines) - line 816

Goal

Refactor each function to extract focused helper routines, bringing all under 50 lines.

Current Status

• All functions compile and tests pass
• No hard limit violations (all under 100 lines)
• Priority: Low (soft limit exceeded, not blocking)

Related

• Parent issue: refactor: reduce function sizes in semantic_function_analysis.f90 to meet soft limit #1929
• Completed work: fix: refactor subroutine parameter analysis (partial fix for #1929) #1940 (subroutine analysis functions)