Add Extended GCD operation

[p-leriche]

Description

Implements the Extended Euclidean Algorithm, computing the greatest common divisor (GCD) and Bézout coefficients for two integers.

Changes

• Add ExtendedGCD.mjs operation
• Update Categories.json to include Extended GCD in Arithmetic/Logic category

Functionality

Finds integers x and y such that: a·x + b·y = gcd(a, b)

This is fundamental for:

• Modular inverse computation
• Solving linear Diophantine equations
• RSA key generation
• Other number theory applications

Features

• Supports decimal and hexadecimal input (0x prefix)
• Handles arbitrarily large integers using BigInt
• Iterative implementation (no recursion limits)
• Clear output showing GCD, Bézout coefficients, and verification equation
• Output formatted for readability with crypto-grade large integers

Dependencies

Depends on #2205

Testing

• Tested with small coprime integers
• Tested with non-coprime integers
• Tested with crypto-grade large integers (2048+ bit)
• Verified mathematical correctness (a·x + b·y = gcd)
• Built successfully with npm run build