Fix function scope

[SIGMazer]

Description

This pull request introduces several enhancements and fixes to the codebase, primarily focusing on function handling, scope management, and debugging capabilities. The most important changes include adding a debug build target, improving function call handling, and updating test cases to reflect new functionality.

Build System Improvements:

• Added DEBUG_FLAGS := -g to Makefile and introduced a new debug target for compiling debug builds with GDB support. [1] [2]

Function Handling Enhancements:

• Added support for function calls in get_expression_type by looking up the function's return type in the symbol table.
• Implemented enter_function_scope to handle function scope entry and parameter assignment, replacing the previous manual parameter handling in execute_function_call. [1] [2]
• Modified handle_return_statement to clean up all scopes until the function scope is reached.

Scope Management:

• Updated get_variable to return NULL if the current scope is a function scope, ensuring proper variable resolution.
• Added is_function_scope to the Scope structure to differentiate function scopes from other scopes.

Test Case Updates:

• Added new test cases fib.brainrot and func_scope.brainrot to verify the correct behavior of recursive functions and function scope handling. [1] [2]
• Updated expected_results.json to include expected outputs for the new test cases.

Related Issue

#115

Fixes #<issue_number>

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Performance improvement
• Refactor

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have documented my changes in the code or documentation
• I have added tests that prove my changes work (if applicable)
• I have run the unit tests locally
• I have run the valgrind memory tests locally
• All new and existing tests pass