feat(collections/unstable): add interleave

[tomas-zijdemans]

interleave merges multiple arrays into a single flat array by round-robin picking one element from each source in turn.

Given [1, 2, 3] and ["a", "b"]:

• zip produces [[1,"a"], [2,"b"]] (3 is dropped)
• interleave produces [1, "a", 2, "b", 3] (nothing dropped)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.17%. Comparing base (4936f23) to head (edbebd2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7010   +/-   ##
=======================================
  Coverage   94.16%   94.17%           
=======================================
  Files         618      619    +1     
  Lines       48802    48824   +22     
  Branches     8601     8609    +8     
=======================================
+ Hits        45954    45978   +24     
+ Misses       2779     2777    -2     
  Partials       69       69           

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