Add NewMapOfWithHasher function

[puzpuzpuz]

Adds NewMapOfWithHasher function to support custom hash functions:

m := NewMapOfWithHasher[int, int](func(i int, _ uint64) uint64 {
	// Murmur3 finalizer. No DDOS protection as it does not support seed.
	h := uint64(i)
	h = (h ^ (h >> 33)) * 0xff51afd7ed558ccd
	h = (h ^ (h >> 33)) * 0xc4ceb9fe1a85ec53
	return h ^ (h >> 33)
})

Some custom hash functions may be faster than the built-in function if the lack of DDOS protection is fine.

Murmur3 finalizer:

BenchmarkMapOfInt_Murmur3Finalizer_WarmUp/reads=100%-8         	525864650	         2.240 ns/op	 446360938 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_Murmur3Finalizer_WarmUp/reads=99%-8          	383333918	         3.127 ns/op	 319827294 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_Murmur3Finalizer_WarmUp/reads=90%-8          	267635385	         4.535 ns/op	 220506863 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_Murmur3Finalizer_WarmUp/reads=75%-8          	181292007	         6.448 ns/op	 155092697 ops/s	       2 B/op	       0 allocs/op

Built-in hash function:

BenchmarkMapOfInt_WarmUp/reads=100%-8         	431097415	         2.858 ns/op	 349837551 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_WarmUp/reads=99%-8          	307244330	         3.951 ns/op	 253072903 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_WarmUp/reads=90%-8          	226392990	         5.306 ns/op	 188477583 ops/s	       0 B/op	       0 allocs/op
BenchmarkMapOfInt_WarmUp/reads=75%-8          	159236962	         7.513 ns/op	 133108546 ops/s	       2 B/op	       0 allocs/op

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.55%. Comparing base (55a8a3a) to head (03661d7).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #137      +/-   ##
==========================================
+ Coverage   97.87%   98.55%   +0.68%     
==========================================
  Files           8        8              
  Lines        1174     1174              
==========================================
+ Hits         1149     1157       +8     
+ Misses         21       14       -7     
+ Partials        4        3       -1     

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