fix(advanced): close the code interpreter REPL at exit (0.16 line)

[radu-mocanu]

Summary

• an advanced agent process with the code interpreter enabled now exits when its run is over, so the job is reported as suspended instead of staying in Running forever
• releases the 0.16 line as 0.16.21 (pyproject + uv.lock) so CD publishes on merge

Why

cherry-pick of #1099 onto release/uipath-langchain-0.16.16, whose tip is the 0.16.20 pinned by the s202 payload. langchain-quickjs 0.3.7 closes its QuickJS contexts from __del__ by blocking on its daemon worker thread, which no longer runs at interpreter finalization, so the process hangs on exit and the robot never learns the job suspended or finished. Only the version lines conflicted, the code and test hunks applied unchanged.

Verified on this branch: tests/agent/advanced/test_code_interpreter.py 36 passed with langchain-quickjs 0.3.7 resolved (the version carrying the __del__ behaviour), ruff and mypy clean.

[Copilot]

🟢 Approval recommended

The change is narrowly scoped, adds explicit regression coverage for the new behavior, and aligns the release version bumps consistently.

Pull request overview

This PR backports a fix to the 0.16 release line to ensure advanced-agent processes using the code interpreter can terminate cleanly (so runs don’t stay “Running” forever), and bumps the package version for release publishing.

Changes:

• Register the code interpreter REPL registry cleanup via atexit to avoid hangs caused by upstream __del__ behavior during interpreter finalization.
• Add a unit test asserting the atexit.register(...) hook is installed by the middleware factory.
• Bump uipath-langchain version to 0.16.21 in both pyproject.toml and uv.lock.

File summaries

File	Description
src/uipath_langchain/agent/advanced/code_interpreter.py	Registers REPL registry closure via atexit when building the code interpreter middleware.
tests/agent/advanced/test_code_interpreter.py	Adds a test to verify the REPL registry close method is registered with atexit.
pyproject.toml	Version bump to 0.16.21 for release.
uv.lock	Lockfile version update to 0.16.21 for release consistency.

Review details

• Files reviewed: 3/4 changed files
• Comments generated: 0
• Review effort level: Lite

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[sonarqubecloud]

Quality Gate failed

Failed conditions
75.0% Coverage on New Code (required ≥ 90%)

See analysis details on SonarQube Cloud