Rewrite pkg/cache, pkg/sync/map to use generics

[Danielius1922]

No description provided.

[codecov-commenter]

Codecov Report

Merging #352 (05c45d2) into master (0375d80) will increase coverage by 0.65%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master     #352      +/-   ##
==========================================
+ Coverage   69.67%   70.32%   +0.65%     
==========================================
  Files          67       68       +1     
  Lines        5675     5780     +105     
==========================================
+ Hits         3954     4065     +111     
+ Misses       1314     1307       -7     
- Partials      407      408       +1     

Impacted Files	Coverage Δ
message/status/status.go	0.00% <ø> (ø)
udp/client/clientconn.go	71.90% <ø> (ø)
udp/server.go	82.22% <ø> (-1.78%)	⬇️
dtls/client.go	78.37% <20.00%> (+2.72%)	⬆️
tcp/clientconn.go	69.17% <30.00%> (+0.97%)	⬆️
dtls/server.go	84.00% <100.00%> (ø)
pkg/sync/map.go	100.00% <100.00%> (ø)
tcp/server.go	81.28% <100.00%> (ø)
udp/client.go	84.21% <100.00%> (-0.54%)	⬇️
udp/client/clientobserve.go	67.24% <100.00%> (ø)
... and 3 more

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