Memory optimization internal blacklist/whitelist cache (#513)

[0xERR0R]

• removed temporary map which was used to eliminate duplicates
• removed temporary step to create a sorted slice

Benchmark before/after:

# before
BenchmarkStringCache-16   282   4215279 ns/op   2319853 B/op   10862 allocs/op

# after
BenchmarkStringCache-16   310   3751947 ns/op    796616 B/op   10271 allocs/op

closes #513

[codecov]

Codecov Report

Merging #514 (9a5e3d5) into development (651ab87) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           development     #514      +/-   ##
===============================================
- Coverage        93.84%   93.83%   -0.01%     
===============================================
  Files               36       36              
  Lines             3085     3081       -4     
===============================================
- Hits              2895     2891       -4     
  Misses             142      142              
  Partials            48       48              

Impacted Files	Coverage Δ
util/common.go	97.87% <ø> (-0.30%)	⬇️
cache/stringcache/string_caches.go	100.00% <100.00%> (ø)

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