The square root operator implementation for fixed-point numbers

[blewater]

• Added the core sqrt function to Fixed, calculating the scaled square root and remainder.
• Uses i128 for intermediate calculations (t = input.0 * SCALE_FACTOR) to avoid overflow.
• Includes int_sqrt helper using Newton's method for u64.
• Lots of unit tests for operator and constraint evaluation.

eval_fixed_sqrt Constraint (eval.rs):
Enforces the constraint out^2 + rem = input * SCALE_FACTOR