Add optimised findfirst etc

[jakobnissen]

The default methods needlessly boundscheck, which can be a serious performance concern.

TODO:

• Memrchr based method
• Fix ambiguity w. base on nightly
• Add an optimised method when iszero is the function

[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.34%. Comparing base (cbab8ab) to head (d430114).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/basic.jl	96.29%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
- Coverage   98.96%   98.34%   -0.63%     
==========================================
  Files           5        5              
  Lines         194      242      +48     
==========================================
+ Hits          192      238      +46     
- Misses          2        4       +2     

Flag	Coverage Δ
unittests	98.34% <96.29%> (-0.63%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.