fix: rework priority handling for lists. We now properly schedule list item pages in priority order

[westonpace]

This actually addresses #2753 without requiring changes to the format but it's more complex and requires more bookkeeping than I'd prefer so I want to leave #2753 open to come up with a better solution at some point.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.76923% with 25 lines in your changes missing coverage. Please review.

Project coverage is 79.20%. Comparing base (a9c678d) to head (b5cf7ec).

Files	Patch %	Lines
rust/lance-encoding/src/decoder.rs	82.81%	11 Missing ⚠️
rust/lance-encoding/src/encodings/logical/list.rs	76.47%	4 Missing and 4 partials ⚠️
...ust/lance-encoding/src/encodings/logical/struct.rs	83.33%	3 Missing and 1 partial ⚠️
rust/lance-encoding-datafusion/src/zone.rs	0.00%	1 Missing ⚠️
.../lance-encoding/src/encodings/logical/primitive.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2769      +/-   ##
==========================================
- Coverage   79.21%   79.20%   -0.01%     
==========================================
  Files         227      227              
  Lines       67733    67795      +62     
  Branches    67733    67795      +62     
==========================================
+ Hits        53652    53695      +43     
- Misses      10968    10985      +17     
- Partials     3113     3115       +2     

Flag	Coverage Δ
unittests	79.20% <80.76%> (-0.01%)	⬇️

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