docs: add fraction reduction rule docs

mathy_core/rules/fraction_reduction.md

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+# Fraction Reduction
+
+The `Fraction Reduction` rule simplifies fractions by canceling out common factors in the numerator and denominator. This transformation reduces the complexity of expressions and produces equivalent fractions in their simplest form.
+
+This rule implements the mathematical principle that when a factor appears in both the numerator and denominator of a fraction, it can be canceled out: `(a × c) / (b × c) = a / b`
+
+## Operations
+
+**Numeric Fraction Reduction**
+
+This handles cases where the numerator and denominator contain common numeric factors. For example, `6/3` simplifies to `2`.
+
+**Variable Cancellation**
+
+When the same variable appears in both the numerator and denominator, the rule cancels them out:
+
+- If the powers are equal, the variable is removed completely
+- If the powers differ, the variable remains with the difference of the exponents
+
+For example:
+
+- `(6x) / (3x)` simplifies to `2`
+- `(6x^2) / (3x)` simplifies to `2x`
+
+**Coefficient Reduction**
+
+The rule also handles coefficient reduction in conjunction with variable cancellation. It first factors out common terms, then reduces the numerical coefficient to its simplest form.
+
+For example, `(3x^2) / (6x)` simplifies to `(1/2)x`.
+
+**Exponent Simplification**
+
+When variables with exponents appear in both the numerator and denominator, the rule simplifies by subtracting the exponents.
+
+For example, `x^4 / x^2` simplifies to `x^2`.
+
+## Implementation Details
+
+The rule creates a reduced fraction by:
+
+1. Identifying common factors in the numerator and denominator
+2. Reducing the numeric coefficients to their simplest form using GCD
+3. Handling variable terms by adjusting their exponents appropriately
+4. Constructing a new expression with the simplified terms
+
+### Examples
+
+`rule_tests:fraction_reduction`