feat: support comparison and logical operators with short-circuiting

[hand-burger]

Summary of Changes

This PR adds support for all C relational, equality, and logical operators, complete with short-circuiting logic in code generation.

1. New Operators Added:
   • Comparison: == (Equal), != (NotEqual), < (LessThan), <= (LessEqual), > (GreaterThan), >= (GreaterEqual).
   • Unary Logical: ! (LogicalNot).
   • Binary Logical: && (LogicalAnd), || (LogicalOr).
2. Lexer Upgrades: Added matching for compound tokens (==, !=, <=, >=, &&, ||) and single character operators (<, >, !).
3. Parser Upgrades: Updated the recursive descent precedence levels to match C standard priority:
   parse_expression → LogicalOr → LogicalAnd → Equality → Relational → Additive → Multiplicative → Unary → Primary.
4. LLVM Codegen & Short-Circuiting:
   • Lowered comparisons using LLVM icmp instruction and zero-extended (zext) the resulting i1 type back to standard i32 to match C's boolean integer mapping.
   • Implemented control flow branching (using Basic Blocks and phi nodes) to support standard short-circuit evaluation for && and ||.
5. Testing: Implemented unit tests for lexer, parser, and codegen, as well as comprehensive integration tests verification.