levenshtein: wrap to sha256 for state hashing

[tmc]

This modernizes the dependency management, and replaces the md5 hash in levenshtein which is not allowed in the go fips140 configuration.

This also switches to the upstream mmap-go implementation which has a few fixes not yet in the blevesearch mmap-go fork.

This change has negligible performance impact:

benchstat md5.txt sha256.txt
                                         │   md5.txt   │             sha256.txt              │
                                         │   sec/op    │   sec/op     vs base                │
NewEvalEditDistance1-16                    23.05µ ± 1%   21.95µ ± 1%   -4.76% (p=0.000 n=20)
NewEvalEditDistance2-16                    87.20µ ± 1%   87.35µ ± 5%        ~ (p=0.659 n=20)
NewEditDistance1-16                        23.29µ ± 1%   23.47µ ± 1%        ~ (p=0.174 n=20)
NewEditDistance2-16                        87.40µ ± 0%   89.08µ ± 0%   +1.92% (p=0.000 n=20)
LevenshteinAutomatonBuilder/Distance0-16   1.612µ ± 2%   1.535µ ± 3%   -4.78% (p=0.000 n=20)
LevenshteinAutomatonBuilder/Distance1-16   14.98µ ± 1%   12.16µ ± 1%  -18.82% (p=0.000 n=20)
LevenshteinAutomatonBuilder/Distance2-16   467.4µ ± 1%   372.7µ ± 1%  -20.25% (p=0.000 n=20)
BuildDfa/Distance1-Wordtest-16             14.56µ ± 2%   13.91µ ± 3%   -4.46% (p=0.000 n=20)
BuildDfa/Distance1-Wordfuzzy-16            16.86µ ± 2%   16.51µ ± 2%        ~ (p=0.056 n=20)
BuildDfa/Distance1-Wordsearch-16           21.12µ ± 1%   21.50µ ± 3%        ~ (p=0.199 n=20)
BuildDfa/Distance2-Wordtest-16             30.73µ ± 2%   31.01µ ± 2%        ~ (p=0.794 n=20)
BuildDfa/Distance2-Wordfuzzy-16            35.68µ ± 5%   36.11µ ± 2%        ~ (p=0.565 n=20)
BuildDfa/Distance2-Wordsearch-16           49.75µ ± 3%   52.48µ ± 4%   +5.49% (p=0.000 n=20)
geomean                                    29.54µ        28.47µ        -3.62%

Fixes #23