refactor: Set up some of the infrastructure for new streaming engine

[ritchie46]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #16900 will improve performances by 21%

_{Comparing skelet (5daf4a1) with main (cd68100)}

Summary

⚡ 1 improvements
✅ 36 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	skelet	Change
⚡	test_groupby_h2oai_q2	5.3 ms	4.4 ms	+21%

[codecov]

Codecov Report

Attention: Patch coverage is 29.85075% with 47 lines in your changes missing coverage. Please review.

Project coverage is 80.99%. Comparing base (6ed624f) to head (5daf4a1).
Report is 1 commits behind head on main.

Files	Patch %	Lines
crates/polars-stream/src/skeleton.rs	0.00%	27 Missing ⚠️
crates/polars-expr/src/planner.rs	0.00%	16 Missing ⚠️
crates/polars-lazy/src/frame/mod.rs	75.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16900      +/-   ##
==========================================
- Coverage   81.44%   80.99%   -0.45%     
==========================================
  Files        1425     1434       +9     
  Lines      187970   189002    +1032     
  Branches     2704     2704              
==========================================
- Hits       153087   153083       -4     
- Misses      34386    35422    +1036     
  Partials      497      497              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.