Add more optimised find methods for BioSequences

[jakobnissen]

This adds SIMD optimised methods for findprev and findnext (and therefore, by extension findfirst and findlast) for the predicates !isgap, iscertain, !iscertain, isambiguous and !isambiguous for the default alphabets for LongSequence and LongSubSeq

The purpose of these is to find e.g. regions of N's in a sequence, or find the first symbol in a long DNA sequence which is not a gap or an unambiguous symbol.

Some benchmarks for AA - nucleotide benchmarks are even better:

s = randaaseq(100_000)
@btime findfirst(isgap, s)
@btime findfirst(isambiguous, s)
@btime findfirst(!iscertain, s)
for i in eachindex(s)
   s[i] = AA_B
end
@btime findfirst(!isambiguous, s)
@btime findfirst(iscertain, s)

Before:
1.738 μs (0 allocations: 0 bytes)
39.195 μs (0 allocations: 0 bytes)
39.195 μs (0 allocations: 0 bytes)
39.205 μs (0 allocations: 0 bytes)
39.205 μs (0 allocations: 0 bytes)

After:
1.894 μs (0 allocations: 0 bytes)
3.270 μs (0 allocations: 0 bytes)
5.500 μs (0 allocations: 0 bytes)
3.240 μs (0 allocations: 0 bytes)
4.530 μs (0 allocations: 0 bytes)

[codecov]

Codecov Report

Attention: Patch coverage is 99.36709% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.87%. Comparing base (95d9218) to head (0d48bdf).
Report is 19 commits behind head on master.

Files with missing lines	Patch %	Lines
src/biosequence/find.jl	96.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #331      +/-   ##
==========================================
+ Coverage   90.87%   91.87%   +0.99%     
==========================================
  Files          31       29       -2     
  Lines        2400     2805     +405     
==========================================
+ Hits         2181     2577     +396     
- Misses        219      228       +9     

Flag	Coverage Δ
unittests	91.87% <99.36%> (+0.99%)	⬆️

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