feat: Add row index to new streaming multiscan

[coastalwhite]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 86.59218% with 24 lines in your changes missing coverage. Please review.

Project coverage is 79.88%. Comparing base (d15bfe5) to head (99856a6).
Report is 45 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/io_sources/csv.rs	48.88%	23 Missing ⚠️
.../polars-stream/src/nodes/io_sources/parquet/mod.rs	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21169      +/-   ##
==========================================
- Coverage   79.88%   79.88%   -0.01%     
==========================================
  Files        1593     1593              
  Lines      227640   227752     +112     
  Branches     2600     2600              
==========================================
+ Hits       181856   181933      +77     
- Misses      45187    45222      +35     
  Partials      597      597              

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