feat(Itertools): add strip_prefix and strip_prefix_by methods

[SAY-5]

Adds strip_prefix and strip_prefix_by to the Itertools trait, the iterator analogue of str::strip_prefix, as discussed in #1096. strip_prefix is implemented in terms of strip_prefix_by, which takes an equality predicate so the prefix items may differ in type from Self::Item. Includes doctests and quickcheck tests that assert parity with str::strip_prefix.

Closes #1096

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.03%. Comparing base (6814180) to head (7a655bf).
⚠️ Report is 202 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
- Coverage   94.38%   94.03%   -0.36%     
==========================================
  Files          48       51       +3     
  Lines        6665     6657       -8     
==========================================
- Hits         6291     6260      -31     
- Misses        374      397      +23     

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[phimuemue]

Hi there, thanks for this.

Regarding the API: Currently this only returns Some(self_after_prefix_removal) on success, but the failure case may be equally interesting for callers.

Can we - instead of Option<Self> - return a Result<Self, (Self, Self::Item, J::Item, J)>, where the Ok case resembles the prefix-removed iterator, and the Err case holds all cheaply-obtainable components that may be of interest for the caller?

• prefix-partially-removed iterator (Self)
• mismatched items (Self::Item vs J::Item)
• remaining prefix (J)

Returning a bespoke struct for the error case may be viable, too.

[SAY-5]

Makes sense, the failure case is worth exposing. I'll switch the return type to Result<Self, (Self, Self::Item, J::Item, J)> so callers can recover the partially-consumed iterators and the mismatched items. Will push the reworked version shortly.