🔧 chore: bump python package to 0.2.1 (pins Julia v0.1.6)

[mpf]

Why

py-v0.2.0 was tagged at commit 30b2655 — the v0.1.5 merge — and published to PyPI at
00:12 UTC, before v0.1.6 existed. The released wheel therefore pins =0.1.5:

{"packages": {"DualPerspective": {"version": "=0.1.5"}}}

That install works — users get the reset! fix — but not the v0.1.6 SequentialSolve status
fix, so Solution.status still comes back 'unknown' on successful solves. PyPI does not
allow replacing a released version, so the corrected pin ships as 0.2.1.

What

Only the version number. The =0.1.6 pin is already on main from #31; the sole diff
between the published tag and main under pypi/ was that one line.

Verified

Built the wheel, installed it into a clean venv with an empty JULIA_DEPOT_PATH and no dev
override, so juliapkg resolved the pin from the registry:

python: 0.2.1 | julia: 0.1.6
Solution(status='optimal', n=40, iterations=5, optimality=1.463e-12, elapsed_time=1.192s)

status='optimal' — which is the whole point of the bump.

Release

After merge: git tag py-v0.2.1 && git push origin py-v0.2.1. v0.1.6 is already registered
and propagated, so the pin resolves immediately.