Add range function into the cache

[lubo-svk]

No description provided.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #399 (9a4b5b0) into master (5032ea4) will increase coverage by 0.29%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #399      +/-   ##
==========================================
+ Coverage   70.45%   70.74%   +0.29%     
==========================================
  Files          68       68              
  Lines        5760     5747      -13     
==========================================
+ Hits         4058     4066       +8     
+ Misses       1296     1282      -14     
+ Partials      406      399       -7     

Impacted Files	Coverage Δ
pkg/cache/cache.go	94.44% <100.00%> (+30.44%)	⬆️
udp/options.go	58.26% <0.00%> (-3.45%)	⬇️
net/conn.go	82.81% <0.00%> (-3.13%)	⬇️
tcp/clientobserve.go	65.00% <0.00%> (-2.23%)	⬇️
udp/client/clientobserve.go	71.84% <0.00%> (+1.15%)	⬆️
udp/client/mux.go	88.88% <0.00%> (+1.38%)	⬆️
dtls/server.go	86.90% <0.00%> (+1.78%)	⬆️
tcp/optionmux.go	88.23% <0.00%> (+3.61%)	⬆️
udp/discover.go	62.50% <0.00%> (+7.95%)	⬆️

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