test: test for map forwarder using simple buffer

[vaibhavtiwari33]

What this PR does / why we need it

test for map forwarder using simple buffer

Testing

The PR aims to add further tests

[codecov]

Codecov Report

❌ Patch coverage is 95.79350% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.08%. Comparing base (6e9f6b2) to head (0de74a9).

Files with missing lines	Patch %	Lines
...aflow-core/src/pipeline/forwarder/map_forwarder.rs	98.04%	10 Missing ⚠️
rust/numaflow-testing/src/simplebuffer/buffer.rs	0.00%	6 Missing ⚠️
...ust/numaflow-core/src/pipeline/isb/simplebuffer.rs	0.00%	3 Missing ⚠️
rust/numaflow-testing/src/simplebuffer.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3270      +/-   ##
==========================================
+ Coverage   80.89%   81.08%   +0.18%     
==========================================
  Files         316      316              
  Lines       72167    72690     +523     
==========================================
+ Hits        58383    58940     +557     
+ Misses      13234    13195      -39     
- Partials      550      555       +5     

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