feat: add an optional process-wide limit for IOPS

[westonpace]

This also fixes a bug where we were not shutting down the I/O loop which would eventually lead to a small memory leak.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.77778% with 19 lines in your changes missing coverage. Please review.

Project coverage is 77.77%. Comparing base (f48e970) to head (645bc68).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance-io/src/scheduler.rs	57.77%	11 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2928      +/-   ##
==========================================
- Coverage   77.81%   77.77%   -0.05%     
==========================================
  Files         231      231              
  Lines       70259    70485     +226     
  Branches    70259    70485     +226     
==========================================
+ Hits        54672    54819     +147     
- Misses      12693    12771      +78     
- Partials     2894     2895       +1     

Flag	Coverage Δ
unittests	77.77% <57.77%> (-0.05%)	⬇️

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[wjones127]

Why not a semaphore?

[westonpace]

Good idea. Switched to a sempahore which simplified things a bit.