Implement with_hasher adaptors

[424ever]

Closes #998

Implementations for the following methods:

• duplicates_with_hasher
• duplicates_by_with_hasher
• unique_with_hasher
• unique_by_with_hasher
• all_unique_with_hasher
• into_group_map_with_hasher
• into_group_map_by_with_hasher
• into_grouping_map_with_hasher
• into_grouping_map_by_with_hasher
• counts_with_hasher
• counts_by_with_hasher

[jswrenn]

One small nit, but otherwise this LGTM.

[phimuemue]

Two nits:

• I'm a bit unhappy about duplicated tests. We can leave them as is and add a TODO that we'd ideally want to write all test cases once and apply them to both normal and _with_hasher functions automagically.

• (Possibly over-nitpicky:) Should we rely on the fact that RandomState is the default BuildHasher or should we extract it so that std can do whatever it wants and we just adapt it? Could be done as follows:

  trait THashMap {
      type BuildHasher;
  }
  impl<K, V, S> THashMap for std::collections::HashMap<K, V, S> {
      type BuildHasher = S;
  }
  type StdDefaultBuildHasher = <std::collections::HashMap<(), ()> as THashMap>::BuildHasher;
  
  

@jswrenn Feel free to proceed as you deem appropriate.

[codecov]

Codecov Report

❌ Patch coverage is 99.52830% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.86%. Comparing base (6814180) to head (194357b).
⚠️ Report is 185 commits behind head on master.

Files with missing lines	Patch %	Lines
src/grouping_map.rs	95.45%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1007      +/-   ##
==========================================
- Coverage   94.38%   93.86%   -0.53%     
==========================================
  Files          48       51       +3     
  Lines        6665     6633      -32     
==========================================
- Hits         6291     6226      -65     
- Misses        374      407      +33     

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[jswrenn]

• Should we rely on the fact that RandomState is the default BuildHasher or should we extract it so that std can do whatever it wants and we just adapt it?

It would be a breaking change for Rust to change its default hasher, so we're fine to rely on RandomState directly.

[xtqqczze]

@424ever Are you planning to continue with this PR?

[424ever]

@424ever Are you planning to continue with this PR?

Sorry for the late reply. Yes, I'll rebase this and clean it up a bit

[424ever]

Do I need to do something about the failing semver checks? Those aren't in any files this PR touches.

[xtqqczze]

@phimuemue @jswrenn Can we get this in for 0.15?

[xtqqczze]

Do I need to do something about the failing semver checks?

The semver check failure is informational, and expected because there are changes to the public API.

[jswrenn]

@phimuemue @jswrenn Can we get this in for 0.15?

Yeah, sure! :)