Expand range sampling from the original u32-only helper to all primitive
integer widths. The new gen_range_<int> methods cover 0..n sampling, while
matching gen_range_<int>_in methods accept standard RangeBounds forms such as
exclusive, inclusive, open-ended, and full-width ranges.
Use rejection sampling against the matching primitive reader for each integer
width. That keeps modulo bias out of the public helpers without introducing a
general RNG trait or depending on rand. Full-width ranges fall back directly to
the primitive reader because their span cannot be represented in the same
integer type.
Document the generated APIs with doctested examples and add a ranges example
that demonstrates unsigned, signed, usize, and full-width sampling.
Test Plan:
- cargo test
- cargo clippy
- cargo clippy --benches
- cargo clippy --tests
- cargo +nightly fmt
Refs: IDEAS.md ergonomics backlog
