optimizations of caches and network stack

[jkralik]

• net: remove set deadlines - goroutines are not wakeup for timeouts
• introduce better cache for expirations

[codecov-commenter]

Codecov Report

Merging #260 (19f488d) into master (d32a1fa) will increase coverage by 3.29%.
The diff coverage is 78.15%.

@@            Coverage Diff             @@
##           master     #260      +/-   ##
==========================================
+ Coverage   60.41%   63.71%   +3.29%     
==========================================
  Files          61       78      +17     
  Lines        4916     5627     +711     
==========================================
+ Hits         2970     3585     +615     
- Misses       1598     1683      +85     
- Partials      348      359      +11     

Impacted Files	Coverage Δ
examples/mcast/client/main.go	0.00% <0.00%> (ø)
net/monitor/inactivity/keepalive.go	91.66% <ø> (ø)
net/options.go	100.00% <ø> (+65.95%)	⬆️
tcp/client.go	4.47% <0.00%> (ø)
udp/client/client.go	10.44% <22.22%> (ø)
tcp/options.go	43.65% <30.00%> (+3.47%)	⬆️
dtls/options.go	46.95% <46.15%> (+8.06%)	⬆️
udp/options.go	58.26% <46.15%> (+18.63%)	⬆️
net/connUDP.go	61.84% <58.33%> (+11.11%)	⬆️
net/dtlslistener.go	70.00% <65.00%> (+70.00%)	⬆️
... and 64 more

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

84.5% Coverage
11.9% Duplication