Clean up bulk_update semantics

[michaelsproul]

In the course of implementing:

• Optimise hdiff buffer handling by (re)using Milhouse data structures lighthouse#9236

I found that bulk_update was a bit of a footgun. It would fail unnecessarily if there were any pending updates, and it would also silently accept invalid updates which would later fail to apply when apply_updates was called.

This PR fixes both of these issues, and adds unit tests and proptests for bulk_update.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.02%. Comparing base (8963bc5) to head (0f11e65).

Files with missing lines	Patch %	Lines
src/list.rs	75.00%	4 Missing ⚠️
src/vector.rs	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
+ Coverage   70.15%   72.02%   +1.86%     
==========================================
  Files          22       22              
  Lines        1280     1301      +21     
==========================================
+ Hits          898      937      +39     
+ Misses        382      364      -18     

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