refactor(rust): Various small fixes for the new streaming engine

[orlp]

Just bumping that failure count down :)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 91 lines in your changes missing coverage. Please review.

Project coverage is 79.82%. Comparing base (19a30ed) to head (4b8662b).
Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/physical_plan/fmt.rs	0.00%	27 Missing ⚠️
crates/polars-stream/src/physical_plan/mod.rs	0.00%	11 Missing ⚠️
crates/polars-stream/src/physical_plan/lower_ir.rs	0.00%	7 Missing ⚠️
crates/polars-stream/src/nodes/in_memory_map.rs	0.00%	6 Missing ⚠️
crates/polars-stream/src/nodes/parquet_source.rs	0.00%	6 Missing ⚠️
crates/polars-stream/src/graph.rs	0.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/reduce.rs	0.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/zip.rs	0.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/multiplexer.rs	0.00%	3 Missing ⚠️
crates/polars-stream/src/nodes/filter.rs	0.00%	2 Missing ⚠️
... and 10 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18384      +/-   ##
==========================================
- Coverage   79.84%   79.82%   -0.03%     
==========================================
  Files        1496     1497       +1     
  Lines      200338   200371      +33     
  Branches     2841     2841              
==========================================
- Hits       159951   159937      -14     
- Misses      39862    39909      +47     
  Partials      525      525              

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