Implement switch statement type checking, interpretation, and tests

[Ypisds]

This PR completes the Switch Statement work for Project 3, covering the type checker fix, interpreter implementation, and interpreter-level tests.

Changes

1. Fix type checker switch case handling

• Updated the switch case literal handling in the type checker.
• Added support for rejecting unsupported case labels such as float and str.
• Prevents Rust from failing compilation due to a non-exhaustive match.
• Keeps the MiniC rule explicit: switch case labels must be int or bool.

2. Implement switch execution in the interpreter

• Evaluates the switch target expression.
• Executes the first matching case.
• Executes the default branch when no case matches.
• Preserves assignments to variables declared outside the switch.
• Cleans up variables declared inside the switch scope.
• Propagates return correctly from inside switch branches.
• Detects duplicate case labels and reports a runtime error.

3. Add interpreter tests for switch

Added tests covering:

• Integer switch case execution.
• Default branch execution.
• Boolean switch case execution.
• Assignment to outer variables inside switch branches.
• Runtime error for duplicate case labels.