refactor(rust): Remove NotifyReceiver from new-streaming parquet source

[nameexhaustion]

It is not an efficient channel abstraction (it causes unnecessary delay/wakeups) and was not needed, we simply just put the morsel_stream_starter into the metadata task

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 87 lines in your changes missing coverage. Please review.

Project coverage is 79.85%. Comparing base (04d0978) to head (74bf5de).
Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/parquet_source.rs	0.00%	87 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18540      +/-   ##
==========================================
- Coverage   79.87%   79.85%   -0.02%     
==========================================
  Files        1501     1500       -1     
  Lines      201823   201800      -23     
  Branches     2868     2868              
==========================================
- Hits       161200   161149      -51     
- Misses      40077    40105      +28     
  Partials      546      546              

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