precompiles: Add EC mixed-add formula

[chfast]

Another -10% time reduction.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.80%. Comparing base (ad6e906) to head (4f394a0).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1170      +/-   ##
==========================================
+ Coverage   94.79%   94.80%   +0.01%     
==========================================
  Files         172      172              
  Lines       19537    19580      +43     
==========================================
+ Hits        18520    18563      +43     
  Misses       1017     1017              

Flag	Coverage Δ
eest_gmp	15.36% <0.00%> (-0.04%)	⬇️
eof_execution_spec_tests	2.55% <0.00%> (-0.01%)	⬇️
ethereum_tests	21.20% <95.74%> (+0.15%)	⬆️
ethereum_tests_silkpre	18.39% <95.65%> (+0.18%)	⬆️
execution_spec_tests	18.18% <0.00%> (-0.05%)	⬇️
unittests	92.54% <100.00%> (+0.01%)	⬆️

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Files with missing lines	Coverage Δ
lib/evmone_precompiles/bn254.cpp	100.00% <100.00%> (ø)
lib/evmone_precompiles/ecc.hpp	100.00% <100.00%> (ø)
lib/evmone_precompiles/secp256k1.cpp	100.00% <100.00%> (ø)

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[rodiazet]

Nice