implement Integer#gcd and Integer#lcm methods in mruby-numeric-ext with full
support for both regular integers and bigints.
key changes:
- add mrb_int_gcd euclidean algorithm for regular integer gcd calculation
- implement int_gcd and int_lcm methods with proper type checking and bigint fallback
- add mrb_bint_gcd, mrb_bint_lcm, mrb_bint_abs functions to bigint api
- register gcd and lcm methods with integer class
- add comprehensive test coverage for both regular and bigint cases
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
fe4ed7e68d