docs: update ergonomics backlog

Refresh IDEAS.md after the ergonomic API pass so the backlog no longer lists
implemented items as open work. Split the remaining ideas into deferred and
still-open groups to record which omissions were deliberate crate-scope choices.

This keeps the project notes aligned with the public API and captures the
reasoning for not adding globals, shuffle, or password presets yet.

Test Plan:
- Not run; documentation-only change.

Refs: IDEAS.md ergonomics backlog

IDEAS.md

@@ -1,15 +1,27 @@
 # Ergonomy ideas
 
-- `Default` / `thread_local` global: `ez_urandom::random_u64()` without
-  constructing or threading an `OsRandom`.
-- `gen_range` for all int widths (currently only `u32`) plus a `Range` /
-  `RangeInclusive` overload.
-- `fill_bytes(&mut [u8])` convenience so callers don't need to import
+- Implemented:
+  - `Default` for infallible convenience construction.
+  - `fill_bytes(&mut [u8])` convenience so callers don't need to import
     `io::Read`.
+  - `gen_range_<int>` for all primitive integer widths.
+  - `gen_range_<int>_in` for standard `RangeBounds` forms, including `Range`
+    and `RangeInclusive`.
+  - `choose<T>(&[T]) -> &T` for generic slice selection.
+  - `Clone` plus fallible `try_clone()` so multiple call sites can own separate
+    handles without adding interior mutability.
+  - Presets for direct alphabet names: `OsRandom::token(len)`, `::hex(len)`,
+    and `::pin(len)`.
+
+- Deferred to keep the crate small:
+  - `thread_local` global helpers like `ez_urandom::random_u64()` without
+    constructing or threading an `OsRandom`.
+  - `shuffle(&mut [T])`; `choose` covers the smaller selection use case without
+    growing into collection algorithms.
+  - `OsRandom::password(len)`; password generation needs policy decisions about
+    symbols, ambiguous characters, and service-specific constraints.
+
+- Still open for later consideration:
 - `bool()` / `f64()` (unit interval) helpers.
-- `shuffle(&mut [T])` and `choose<T>(&[T]) -> &T` — generic, not just bytes.
 - Accept a `&str` alphabet directly (not just `&[u8]`) and drop the ASCII
   assert by iterating `chars()`.
-- Loosen `&mut self` to `&self` via interior buffering, or impl `Clone`, so
-  multiple call sites don't fight the borrow checker.
-- Builder / presets: `OsRandom::password(len)`, `::hex(len)`, `::token(len)`.