enhance WorkflowRuntime and WorkflowRuntimeBuilder with close handlig and lifecycle management

[matheusandre1]

Description

two problems that prevented a clean full restart of WorkflowRuntime (for example on a Quarkus dev-mode live reload or between tests)

• WorkflowRuntime.close() blocked for the full 60 second channel timeout. The channel was shut down gracefully while the worker thread still held the getWorkItems stream open, so awaitTermination never returned early.
• WorkflowRuntimeBuilder.build() kept returning the closed runtime. The static singleton was never released, so a new builder got back the old instance whose channel was already shut down.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Closes: #1734

Related: #1631 (closeNow() proposal, PR #1632) and PR #1727, which fixed the worker loop exit but not this blocking.

RELEASE NOTE: FIX WorkflowRuntime.close() no longer blocks on the open work-item stream, and WorkflowRuntimeBuilder.build() returns a new runtime after the previous one was closed.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.09%. Comparing base (d5c3c62) to head (447544c).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1816      +/-   ##
============================================
+ Coverage     78.99%   79.09%   +0.09%     
- Complexity     2591     2600       +9     
============================================
  Files           264      264              
  Lines          7770     7778       +8     
  Branches        815      818       +3     
============================================
+ Hits           6138     6152      +14     
+ Misses         1269     1266       -3     
+ Partials        363      360       -3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.