fix: dispose IProcessInvoker in Docker/Container/UnixUtil call sites

[herbenderbler]

Summary

IProcessInvoker instances created via HostContext.CreateService<IProcessInvoker>() in a few Docker/container/unix paths were not disposed.
Because CreateService returns a new instance per call, those paths could retain process-related resources longer than needed on long-lived runners.

What Changed

• Wrapped per-call IProcessInvoker usage in using scopes in:
  • src/Runner.Worker/Container/DockerCommandManager.cs
  • src/Runner.Worker/ContainerOperationProvider.cs
  • src/Runner.Common/Util/UnixUtil.cs
• Kept existing output/error handler behavior and call semantics intact.
• Added focused L0 coverage in:
  • src/Test/L0/ProcessInvokerDisposalL0.cs
  • src/Test/L0/Util/UnixUtilL0.cs

Why This Is Safer

• Ensures invoker disposal is deterministic per invocation.
• Reduces risk of resource retention in hot Docker/container code paths.
• Preserves existing runtime behavior (command execution, output capture, cancellation flow).

Test Plan

• L0 tests validate disposal on success and exception paths.
• git diff --check and IDE lints are clean.

[Copilot]

Pull request overview

Fixes a managed-memory/resource leak in runner container/unix execution paths by ensuring IProcessInvoker instances created via HostContext.CreateService<IProcessInvoker>() are properly disposed after use.

Changes:

• Wrap IProcessInvoker creation in using blocks across Docker/container execution and UnixUtil.ExecAsync.
• Add L0 tests to verify CreateService<IProcessInvoker>() results are disposed (including exception paths).
• Add PR-audit documentation and adjust .gitignore.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Runner.Worker/Container/DockerCommandManager.cs	Dispose per-call IProcessInvoker instances in docker command execution paths.
src/Runner.Worker/ContainerOperationProvider.cs	Dispose per-call IProcessInvoker in ExecuteCommandAsync output-capture path.
src/Runner.Common/Util/UnixUtil.cs	Dispose per-call IProcessInvoker in ExecAsync, keeping handler unsubscribe safety.
src/Test/L0/ProcessInvokerDisposalL0.cs	Adds disposal-pattern tests for CreateService + using and exception paths.
src/Test/L0/Util/UnixUtilL0.cs	Adds UnixUtil-focused disposal verification tests on non-Windows.
PR_DESCRIPTION_F1.md	Adds a PR/audit write-up describing the leak and fix.
.gitignore	Adjusts ignore patterns (currently impacts Rider .DotSettings.user ignores).