Refactor parser and lexer logic into new src/parser library

[wizard7377]

Is your feature request related to a problem? Please describe.
Currently, the parser and lexer logic reside in src/frontend and their implementation is somewhat inconsistent, making it less maintainable and harder to work with across different parts of the codebase.

Describe the solution you'd like
Move all parser and lexer logic from src/frontend to a new library directory, src/parser.
Ensure the parsing logic is made more consistent, with clear interfaces and easier maintainability. This should include:

• Consolidating duplicated parser/lexer code.
• Improving naming conventions and structure within src/parser.
• Providing documentation for interfaces.

Describe alternatives you've considered

• Keeping the current structure but refactoring for clarity.
• Breaking out just the lexer or parser separately.

Additional context
This effort is intended to pave the way for further expansions or simplifications of parsing logic, and to ease onboarding for contributors.