Replace per-job cache key prefixes (uv-lint-, uv-typecheck-, uv-security-,
uv-quality-, uv-tests-, uv-coverage-) with a single shared key
uv-${{ hashFiles('pyproject.toml') }} across all jobs in ci.yml.
Also add a missing uv cache step to the build job and add uv caching
to nightly-quality.yml, which previously had no cache at all.
All jobs now share the same cache entry when pyproject.toml is unchanged,
eliminating redundant package downloads and reducing CI wall-clock time.
ISSUES CLOSED: #1535
freemo