style: apply rustfmt, add clippy lint suppressions, and code cleanup

[LunaStev]

This PR introduces a comprehensive cleanup of the codebase to improve maintainability and ensure consistent coding standards. It focuses on automated formatting, silencing non-critical lint warnings, and applying idiomatic Rust improvements. No functional logic or behavioral changes are included.

Key Changes

1. Code Formatting:

   • Applied rustfmt project-wide to standardize indentation, bracing, and multi-line function signatures.
   • Fixed several instances of No newline at end of file.

2. Lint Management:

   • Added module-level #![allow(...)] attributes to lexer, parser, and llvm_temporary modules.
   • This suppresses warnings for dead_code, unused_variables, and specific Clippy lints (e.g., type_complexity, collapsible_if) to reduce noise during the current development phase.

3. Idiomatic Rust Refactoring:

   • Character Checks: Replaced .is_digit(10) with .is_ascii_digit() and .is_digit(16) with .is_ascii_hexdigit() for better performance and clarity.
   • Iterators: Simplified .lines().nth(0) to .lines().next().
   • Imports: Reorganized and grouped use statements across all impacted files.
   • Error Messages: Refactored eprintln! and panic! calls in the lexer and parser to follow a more consistent format.

4. Refactoring for Readability:

   • Updated complex match arms and long if-let chains into more readable multi-line blocks.
   • Standardized the internal helper methods and token creation logic.