LRU cache utility

[chfast]

Adds generic single-threaded implementation of
the least recently used (LRU) cache.

This is to be used to cache the code and code analysis.

[codecov]

Codecov Report

Attention: Patch coverage is 72.96296% with 73 lines in your changes missing coverage. Please review.

Project coverage is 93.98%. Comparing base (81c9dda) to head (2938377).

Files with missing lines	Patch %	Lines
test/internal_benchmarks/lru_cache_bench.cpp	0.00%	70 Missing ⚠️
lib/evmone/lru_cache.hpp	93.93%	2 Missing ⚠️
test/unittests/lru_cache_test.cpp	99.40%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1090      +/-   ##
==========================================
- Coverage   94.31%   93.98%   -0.33%     
==========================================
  Files         159      162       +3     
  Lines       17221    17491     +270     
==========================================
+ Hits        16242    16439     +197     
- Misses        979     1052      +73     

Flag	Coverage Δ
eof_execution_spec_tests	23.25% <0.00%> (-0.37%)	⬇️
ethereum_tests	26.22% <0.00%> (-0.41%)	⬇️
ethereum_tests_silkpre	18.62% <0.00%> (-0.33%)	⬇️
execution_spec_tests	20.63% <0.00%> (-0.33%)	⬇️
unittests	88.83% <73.50%> (-0.24%)	⬇️

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

Files with missing lines	Coverage Δ
test/unittests/lru_cache_test.cpp	99.40% <99.40%> (ø)
lib/evmone/lru_cache.hpp	93.93% <93.93%> (ø)
test/internal_benchmarks/lru_cache_bench.cpp	0.00% <0.00%> (ø)