feat: add iter_cow_from for List and Vector

[NikhilSharmaWe]

Fixes: #57

[NikhilSharmaWe]

@michaelsproul Could you please take a look at the changes and share your review?

[michaelsproul]

Looks good

Could you also please look at adding some tests in https://github.com/sigp/milhouse/blob/main/src/tests/proptest/operations.rs

I noticed we don't have tests for regular iter_cow either, but we could get away with just testing iter_cow_from.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.15%. Comparing base (dbe9e15) to head (c532da6).

Files with missing lines	Patch %	Lines
src/vector.rs	37.50%	5 Missing ⚠️
src/list.rs	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
- Coverage   70.38%   70.15%   -0.24%     
==========================================
  Files          22       22              
  Lines        1263     1280      +17     
==========================================
+ Hits          889      898       +9     
- Misses        374      382       +8     

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[NikhilSharmaWe]

@michaelsproul Quick ping on this PR
The requested updates have been made. Would appreciate a follow-up review when time allows.

[michaelsproul]

I'm off until Monday

[michaelsproul]

LGTM, thanks for pushing this along

For future PRs, make sure you run cargo fmt!