refactor: Fix parquet file metadata is dropped after first DSL->IR conversion

[nameexhaustion]

No description provided.

[nameexhaustion]

We had mutexes on multiple fields on the DSL::Scan, I just cache the IR here instead of adding another mutex

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 12 lines in your changes missing coverage. Please review.

Project coverage is 79.84%. Comparing base (5d81d4a) to head (f996d44).
Report is 31 commits behind head on main.

Files with missing lines	Patch %	Lines
...-stream/src/nodes/parquet_source/metadata_fetch.rs	0.00%	6 Missing ⚠️
...ates/polars-plan/src/plans/conversion/dsl_to_ir.rs	63.63%	4 Missing ⚠️
...es/polars-mem-engine/src/executors/scan/parquet.rs	94.44%	1 Missing ⚠️
...ates/polars-stream/src/nodes/parquet_source/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18789      +/-   ##
==========================================
- Coverage   79.84%   79.84%   -0.01%     
==========================================
  Files        1518     1518              
  Lines      205563   205577      +14     
  Branches     2892     2892              
==========================================
+ Hits       164137   164143       +6     
- Misses      40878    40886       +8     
  Partials      548      548              

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[ritchie46]

Can we add a test somehow?

[nameexhaustion]

Can we add a test somehow?

1 special order coming up 😁

[codspeed-hq]

CodSpeed Performance Report

Merging #18789 will not alter performance

_{Comparing nameexhaustion:dsl-ir-metadata (f996d44) with main (5d81d4a)}

Summary

✅ 40 untouched benchmarks

[TNieuwdorp]

This might've fixed the post 1.1.0 regression that was introduced somehow in the dsl_to_ir.rs! 🚀