Capture a short backlog of ergonomy improvements for the public API so the
ideas don't get lost between sessions. This is a planning document only —
no code changes, and nothing here is committed to as a roadmap.
Items recorded:
- Thread-local global helpers (e.g. `random_u64()`) to avoid threading an
`OsRandom` through call sites for one-off uses.
- `gen_range` for all integer widths and `Range`/`RangeInclusive` overloads;
today only `gen_range_u32` exists.
- `fill_bytes(&mut [u8])` so callers don't need to bring `io::Read` into
scope just to fill a buffer.
- `bool()` and `f64()` (unit interval) helpers.
- Generic `shuffle(&mut [T])` and `choose<T>(&[T]) -> &T`, not just byte
slices.
- Accept `&str` alphabets directly and drop the ASCII assert by iterating
`chars()` instead of bytes.
- Loosen `&mut self` to `&self` (interior buffering) or impl `Clone`, so
multiple call sites can share a handle without borrow-checker friction.
- Preset constructors: `OsRandom::password(len)`, `::hex(len)`,
`::token(len)`.
