Prepare 0.10.0 release

[hardbyte]

Bumps Cargo.toml to 0.10.0 (Cargo.lock follows) and dates the CHANGELOG section with a summary paragraph.

Includes since 0.9.0: #44 (clean-install import fix + wheel smoke test), #51 (Context environment caching), #52 (security scan fix, Dependabot, stub alignment), #53/#54 (Dependabot bumps), #55 (naive-datetime docs, refs #50).

Release-notes extraction verified locally with the release job's awk: the ## [0.10.0] section is captured in full and stops before ## [0.9.0].

After merging, the tag push is the manual step:

git fetch origin && git checkout main && git pull --ff-only
git tag -a v0.10.0 -m "v0.10.0" && git push origin v0.10.0

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