[PERF] Make merging of ScanTasks be more conservative when provided with a LIMIT

[jaychia]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #2758 will improve performances by ×8

_{Comparing jay/merge-scan-task-limit-pushdowns (ef5af18) with main (7e134f2)}

Summary

⚡ 2 improvements
✅ 14 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	jay/merge-scan-task-limit-pushdowns	Change
⚡	test_count[1 Small File]	25.8 ms	23.1 ms	+11.36%
⚡	test_show[100 Small Files]	393.5 ms	49.3 ms	×8

[codecov]

Codecov Report

Attention: Patch coverage is 97.56098% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (main@7e134f2). Learn more about missing BASE report.
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/daft-scan/src/scan_task_iters.rs	97.43%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2758   +/-   ##
=======================================
  Coverage        ?   63.23%           
=======================================
  Files           ?      996           
  Lines           ?   113444           
  Branches        ?        0           
=======================================
  Hits            ?    71740           
  Misses          ?    41704           
  Partials        ?        0           

Files with missing lines	Coverage Δ
src/daft-plan/src/physical_planner/translate.rs	91.49% <100.00%> (ø)
src/daft-scan/src/scan_task_iters.rs	96.93% <97.43%> (ø)