test: tests for source forwarder using simple buffer ISB

[vaibhavtiwari33]

What this PR does / why we need it

tests for source forwarder using simple buffer ISB

Testing

this is the test

[codecov]

Codecov Report

❌ Patch coverage is 96.57795% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.95%. Comparing base (6e9f6b2) to head (4ca414d).

Files with missing lines	Patch %	Lines
...ow-core/src/pipeline/forwarder/source_forwarder.rs	96.53%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3283      +/-   ##
==========================================
+ Coverage   80.89%   80.95%   +0.05%     
==========================================
  Files         316      316              
  Lines       72167    72427     +260     
==========================================
+ Hits        58383    58634     +251     
- Misses      13234    13241       +7     
- Partials      550      552       +2     

☔ View full report in Codecov by Sentry.
📢 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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[vigith]

why do we have to make it multi_thread? default is single thread? what will happen if we do not make it multi threaded?

[vaibhavtiwari33]

It should be fine in this case tbh. I added this since the UDSource was to be spawned in a separate os thread, but it will not affect the outcome here if we remove multi-thread

[vigith]

let's figure out why multi_thread is really required only for failure path.