test: Tests for sink forwarder using simple buffer backed ISBs

[vaibhavtiwari33]

What this PR does / why we need it

Tests for sink forwarder using simple buffer backed ISBs

Testing

This is the test

[codecov]

Codecov Report

❌ Patch coverage is 99.01316% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.05%. Comparing base (6e9f6b2) to head (73552e7).

Files with missing lines	Patch %	Lines
...flow-core/src/pipeline/forwarder/sink_forwarder.rs	99.01%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3282      +/-   ##
==========================================
+ Coverage   80.89%   81.05%   +0.15%     
==========================================
  Files         316      316              
  Lines       72167    72471     +304     
==========================================
+ Hits        58383    58741     +358     
+ Misses      13234    13175      -59     
- Partials      550      555       +5     

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