refactor(rust): Fix new-streaming parquet on empty parquet

[nameexhaustion]

No description provided.

[nameexhaustion]

Use an Option instead of being fancy with is_empty(), much more robust

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.87%. Comparing base (4894e24) to head (a6af605).
Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
...tes/polars-stream/src/nodes/parquet_source/init.rs	0.00%	4 Missing ⚠️
...-stream/src/nodes/parquet_source/metadata_fetch.rs	0.00%	1 Missing ⚠️
...ates/polars-stream/src/nodes/parquet_source/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18763      +/-   ##
==========================================
+ Coverage   79.85%   79.87%   +0.02%     
==========================================
  Files        1517     1517              
  Lines      205530   205524       -6     
  Branches     2892     2892              
==========================================
+ Hits       164119   164165      +46     
+ Misses      40863    40811      -52     
  Partials      548      548              

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