Bump every crate (and the python binding) from 0.6.0 to 0.6.1, with all
internal `dashu-*` version requirements synced.

Each crate with changes folds its `## Unreleased` into a `## 0.6.1` section:
the integer small-operand clone/eq/cmp fast paths, the float ×u/×π trig and
hyperbolic families plus the Mag-radius migration's directed-rounding fixes
(#99/#100/#102/#103), and the complex ball-based radius propagation with the
breaking `powi(z, ±1)` precision change. The root changelog aggregates the
same set per crate; its stale `cbig!` entry (already shipped in 0.6.0) is
dropped. Crates without changes get no section.

Co-Authored-By: Claude <noreply@anthropic.com>