ci: Add package verification check

[vdusek]

Summary

Adds an automated end-to-end verification of the built sdist + wheel to guard against the silent failure mode behind #1890 — where artifacts build successfully but crash on install or import.

New: scripts/verify_built_package.py — a standalone script (runnable locally, no crawlee install required) that:

• Validates sdist contents: required metadata files (LICENSE, README.md, CHANGELOG.md, CONTRIBUTING.md, pyproject.toml), no tests/ / docs/ / website/ / .github/ / examples/ leakage, no uv.lock, all 192 .py sources present, all 27 data files (every py.typed, every project_template/**, every _redis/lua_scripts/*.lua) present.
• Validates wheel contents: .dist-info/METADATA present plus the same source + data assertions.
• Installs the wheel into a fresh Python 3.14 venv with [all] extras and runs an import + crawler-construction smoke test.
• Installs the sdist into a fresh venv — this is the load-bearing check, since pip rebuilds the wheel from sdist contents and any missing source surfaces here.
• Runs crawlee create --no-apify --no-install ... and asserts the scaffolded project files exist (catches a silently-dropped project_template/).

Takes ~10s locally, ~1 min in CI. Exits non-zero on any failure.

CI wiring:

• .github/workflows/_check_package.yaml — new reusable workflow that builds + verifies.
• on_pull_request.yaml — runs package_check on every PR (parallel with tests and code_checks).
• manual_release_stable.yaml + manual_release_beta.yaml — inserts a Verify built package step inside the pypi_publish job, between the prepare-distribution and PyPI upload steps. The exact byte-identical artifact about to be uploaded is verified.

Verified locally

• Pass path: clean build → all 5 check groups green, exit 0
• Negative path: tampered sdist with project_template/cookiecutter.json and a .lua script removed → flagged both, exited 1
• actionlint clean on all four workflows

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.84%. Comparing base (0e7402f) to head (5b35186).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1893      +/-   ##
==========================================
+ Coverage   92.82%   92.84%   +0.01%     
==========================================
  Files         167      167              
  Lines       11699    11699              
==========================================
+ Hits        10860    10862       +2     
+ Misses        839      837       -2     

Flag	Coverage Δ
unit	92.84% <ø> (+0.01%)	⬆️

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