Make AppHarness dependencies installable

[harsh21234i]

Summary

Fixes issue #6974 by making reflex.testing usable from a clean published Reflex installation.

Changes

• Removed the top-level uvicorn import from reflex.testing.

• Added lazy imports with actionable installation messages.

• Added a reflex[testing] extra containing:

  • uvicorn
  • psutil
  • selenium

• Updated uv.lock.

• Added a regression test for importing reflex.testing without test dependencies.

• Added a changelog fragment.

Testing

• AppHarness unit tests: 5 passed, 1 skipped
• Verified reflex.testing imports without uvicorn and psutil.
• Ruff formatting and lint checks passed.

[greptile-apps]

Greptile Summary

The PR makes reflex.testing importable without eagerly requiring AppHarness runtime dependencies.

• Adds a testing package extra for psutil, Selenium, and uvicorn.
• Lazily imports uvicorn at every backend and production frontend startup path, with actionable installation errors.
• Adds equivalent missing-dependency guidance for psutil cleanup.
• Adds an import regression test, lockfile update, and changelog fragment.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
reflex/testing.py	Replaces the eager uvicorn import with guarded lazy imports across all runtime uses, resolving the previously reported production harness NameError.
pyproject.toml	Adds the testing extra containing the three optional AppHarness dependencies.
tests/units/test_testing.py	Adds regression coverage confirming that importing reflex.testing does not bind uvicorn at module load.
uv.lock	Synchronizes the package lock metadata with the new testing extra.

_{Reviews (3): Last reviewed commit: "Merge branch 'main' into fix/6974-testin..." | Re-trigger Greptile}

[cubic-dev-ai]

All reported issues were addressed across 5 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[codspeed-hq]

Merging this PR will not alter performance

✅ 32 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing harsh21234i:fix/6974-testing-deps (65263ee) with main (9a26753)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩