Add ProgressiveList to proptest suite

[Copilot]

Adds property-based testing for ProgressiveList in the proptest operations suite.

Changes

• ProgressiveSpec<T> - Specification struct without length limit (no N type parameter), matching ProgressiveList's unbounded nature
• arb_op_progressive - Strategy generating only implemented operations: Len, Push, Iter, TreeHash, Debase
• apply_ops_progressive_list - Applies operations to both ProgressiveList and spec, verifying equivalence
• Test module - Tests for u8, u64, Hash256, and Large types

Example

progressive_list_test!(u8, u8);
progressive_list_test!(hash256, Hash256, arb_hash256());

Unimplemented operations (Get, Set, IterFrom, PopFront, Rebase, etc.) are handled as no-ops for exhaustive matching but excluded from generation.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.02%. Comparing base (07a808e) to head (e32d558).

Additional details and impacted files

@@                 Coverage Diff                  @@
##           progressive-list      #89      +/-   ##
====================================================
+ Coverage             69.35%   73.02%   +3.66%     
====================================================
  Files                    24       24              
  Lines                  1426     1427       +1     
====================================================
+ Hits                    989     1042      +53     
+ Misses                  437      385      -52     

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