feat(primitives): add comprehensive float number support

- Fix arithmetic operators (+, *) to return Float identity values (0.0, 1.0)
- Add type predicates: float? and int? for type checking
- Add type conversions: int->float and float->int
- Add math functions: floor, ceil, round, sqrt, pow, abs, exp, log, sin, cos, tan
- Refactor eval.ml code formatting for better readability
- Add comprehensive float tests in test/13_floats.mlisp

Author: i-shm