chore: release v0.2.1

[tschm]

Release v0.2.0 → v0.2.1 (patch).

Version locations bumped

bump-my-version rewrote only the locations declared in [tool.bumpversion]:

• pyproject.toml — [project].version (anchored pattern, so no [tool.*] table or dependency pin was touched)
• pyproject.toml — [tool.bumpversion].current_version
• uv.lock — the cvx-quadprog package block, so uv sync --locked stays green

Changelog

One new section prepended to CHANGELOG.md; no existing section was modified.

## [0.2.1] - 2026-08-06

### Performance
- Apply the delete step's 2x2 with BLAS rot

### Other Changes
- Merge pull request #12 from Jebel-Quant/perf_blas_rot_delete_chase

Merging this PR does not publish the release

There is no tag yet, deliberately. A squash-merge replaces this branch's commits, so
a tag cut here would name a SHA that never lands on main. The tag is created afterwards
from the merged commit by a second /rhiza:release run, which re-checks that v0.2.1
strictly increases and does not already exist before pushing it. Pushing that tag is what
triggers release CI.