Add and Test Basic U64 Functions

[dellamora]

Implement basic arithmetic and bitwise operations for U64 (Unsigned 64-bit integer). Follow the pattern of existing Nat functions and include bitwise operations.

Tasks

• [ ] Implement basic arithmetic operations: add, sub, mul, div, mod, eq, lt, gt, double, show
• [ ] Implement bitwise operations

[VictorTaelin]

no need for half, also lets add bitwise functions (pretty much all fns that JS implements for u32)