feat(scantask-1): add a config flag for new scantask splitting algorithm

[jaychia]

Adds a new ScanTask splitting algorithm that can be enabled by specifying the environment variable DAFT_SCANTASK_SPLITTING_LEVEL=2

[codspeed-hq]

CodSpeed Performance Report

Merging #3615 will not alter performance

_{Comparing jay/split-all-files-iter (9b0c1df) with main (a76f800)}

Summary

✅ 27 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 59.52381% with 17 lines in your changes missing coverage. Please review.

Project coverage is 77.79%. Comparing base (063de4d) to head (9b0c1df).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/common/daft-config/src/python.rs	25.00%	9 Missing ⚠️
src/daft-scan/src/scan_task_iters/mod.rs	72.00%	7 Missing ⚠️
src/common/daft-config/src/lib.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3615      +/-   ##
==========================================
- Coverage   77.80%   77.79%   -0.02%     
==========================================
  Files         718      718              
  Lines       88250    88270      +20     
==========================================
+ Hits        68666    68672       +6     
- Misses      19584    19598      +14     

Files with missing lines	Coverage Δ
daft/context.py	87.65% <ø> (ø)
src/common/daft-config/src/lib.rs	83.78% <80.00%> (-0.28%)	⬇️
src/daft-scan/src/scan_task_iters/mod.rs	93.96% <72.00%> (ø)
src/common/daft-config/src/python.rs	66.07% <25.00%> (-2.33%)	⬇️

... and 6 files with indirect coverage changes