precompiles: Add expmod benchmarks

[chfast]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.88%. Comparing base (66dcad5) to head (4d2213b).

Files with missing lines	Patch %	Lines
test/precompiles_bench/precompiles_bench.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1196      +/-   ##
==========================================
- Coverage   94.89%   94.88%   -0.01%     
==========================================
  Files         171      171              
  Lines       19680    19681       +1     
==========================================
  Hits        18675    18675              
- Misses       1005     1006       +1     

Flag	Coverage Δ
eof_execution_spec_tests	2.53% <ø> (ø)
ethereum_tests	22.36% <ø> (ø)
ethereum_tests_silkpre	17.87% <0.00%> (-0.01%)	⬇️
execution_spec_tests	19.56% <ø> (ø)
unittests	92.44% <ø> (ø)

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Files with missing lines	Coverage Δ
test/precompiles_bench/precompiles_bench.cpp	0.00% <0.00%> (ø)

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