feat: Build a Mathematical Expression Parser and Evaluator from Scratch (#1673)

[knoxiboy]

📝 Description

Built a zero-external-dependency mathematical expression parser, tokenizer, AST compiler, and evaluator module in Python.

Key additions:

• Tokenizer (\expression_parser/tokenizer.py): Converts math expressions to token streams with support for operators (+, -, *, /, %, ^), implicit multiplication (\2(3+4), \3pi), and standard functions/constants.
• AST Parser (\expression_parser/parser.py): Recursive-descent parser building AST nodes while maintaining correct operator precedence and associativity rules.
• Evaluator (\expression_parser/evaluator.py): Evaluates AST trees with real-domain math functions (\sin, \cos, \ an, \sqrt, \�bs, \log, \exp, \loor, \ceil, \min, \max) and dynamic variable binding.
• CLI & REPL (\expression_parser/main.py): Interactive shell for direct math expression parsing and variable handling.
• Registry Integration (\projects_registry.json): Registered tool under \math\ category for interactive menu discovery.
• Unit Tests (\ ests/test_expression_parser.py): Comprehensive pytest test suite covering tokenizing, precedence, implicit operations, function calls, variables, and error handling.

🔗 Linked Issue

Closes #1673

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📋 Contribution Checklist

• I have verified that my files are placed in the correct directory.
• I have tested my changes thoroughly on my local machine.
• GSSoC 2026: I have been formally assigned to this issue and noted it above.

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