Enhanced polynomial parser with extended mathematical expression support

[RazinShaikh]

This PR significantly expands the capabilities of the symbolic polynomial parser by adding support for four key mathematical expression features that were previously missing.

Changes Made

1. Subtraction Support

• Enhanced grammar with proper add and sub transformations using -> syntax
• Added add() and sub() methods in PolyTransformer for handling + and - operations
• Now supports expressions like a - b, 2*x - 3*y + z

2. Unary Negation Support

• Split term rule into neg_term and pos_term for explicit handling of negative terms
• Added neg_term() and pos_term() transformer methods
• Properly handles expressions like -x, -2*y, -(x+y)

3. Exponentiation (Powers) Support

• Added ^ operator support in the grammar with explicit exponent rule
• Updated factor rule to handle base ("^" exponent)? patterns
• Implemented factor() and exponent() methods in PolyTransformer
• Now supports expressions like x^2, y^3, (x+1)^2

4. Parentheses for Grouping

• Enhanced base rule to include "(" expr ")" for proper expression grouping
• Enables complex nested expressions like 2*(x+y), (a+b)^2, x*(y+z)^3

5. Implicit Multiplication

• Modified grammar to support optional multiplication operator: ("*"? factor)*
• Now accepts natural mathematical notation like 2x, 3xy, 2(x+y) instead of requiring explicit *

6. Decimal Number Support

• Added decimal rule and imported DECIMAL from Lark commons
• Implemented decimal() transformer method using Fraction for precise arithmetic
• Supports expressions with decimal coefficients like 1.5x, 0.25*y^2, 3.14159

Examples of New Supported Expressions

• Basic arithmetic: x + y, a - b, 2*x - 3*y + z
• Negation: -x, -2*y, -(x+y), -x^2 + y
• Powers: x^2 + y^3, 2^3, (x+1)^2
• Grouping: 2*(x+y), (a+b)*(c+d), 3*(x+y)^2
• Implicit multiplication: 2x, 3xy, 2(x+1), πr^2
• Decimals: 1.5x + 0.25y, 3.14159*r^2
• Complex combinations: 2x^2 - 3(y+z)^3 + 1.5, -0.5*π*(r+1)^2

Technical Details

• Uses Lark's native operator precedence with -> transformations for clean parsing
• Maintains backward compatibility with existing expressions
• Leverages Fraction for decimal precision to avoid floating-point errors
• Proper handling of operator precedence ensures mathematical correctness

This enhancement makes the polynomial parser much more user-friendly and capable of handling natural mathematical expressions while maintaining the robust symbolic computation capabilities of the existing system.

Closes zxcalc/zxlive#232 and closes zxcalc/zxlive#353

[jvdwetering]

Nice! Perhaps add some tests to show things it can parse and also how it fails when it gets things it doesn't understand? (probably can be auto-generated by copilot)