feat(collections/unstable): have zip accept Iterable

[tomas-zijdemans]

• Mirrors the iterable-based interleave API so zip can accept any Iterable, not just arrays.
• Non-array iterables are consumed eagerly via Array.from, then the existing index-based zip-to-shortest logic runs.
• Adds a two-iterable fast path matching interleave.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.61%. Comparing base (a496da2) to head (e80670e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7120   +/-   ##
=======================================
  Coverage   94.61%   94.61%           
=======================================
  Files         634      635    +1     
  Lines       51801    51829   +28     
  Branches     9329     9338    +9     
=======================================
+ Hits        49011    49038   +27     
  Misses       2216     2216           
- Partials      574      575    +1     

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[fibibot]

Iterable signature mirrors unstable_interleave, which is the right consistency target. Array.from(it) only runs for non-arrays — actual arrays are passed through, so the no-mutation invariant the stable zip had is preserved (the existing "handles no mutation" test still passes on a generator-free path). Two-iterable fast path matches interleave. CI is green.

• nit: the test file is ~95% a copy of zip_test.ts — fine for now, but if zip ever gets a behaviour fix the duplication will bite. A _zip_shared_test.ts helper would dedupe.
• nit: no test that calls zip with a single non-array iterable (e.g. zip(new Set([1,2,3]))); the multi-iterable Set/generator cases are covered.

[fibibot]

@bartlomieju this is ready to merge