Fix lint issues for golangci-lint v2.10.1

[asayyah]

Summary

• Migrate deprecated dtls.Client/dtls.Listen/dtls.Config to dtls.ClientWithOptions/dtls.ListenWithOptions with functional options (staticcheck SA1019)
• Suppress gosec G115 for intentional uint32→byte truncation in renomination serialization

Test plan

• golangci-lint run ./... passes with 0 issues (v2.10.1)
• go build ./... succeeds

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.49%. Comparing base (bca1b4c) to head (84445d0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #897      +/-   ##
==========================================
+ Coverage   88.40%   88.49%   +0.08%     
==========================================
  Files          44       44              
  Lines        5591     5591              
==========================================
+ Hits         4943     4948       +5     
+ Misses        448      444       -4     
+ Partials      200      199       -1     

Flag	Coverage Δ
go	88.49% <100.00%> (+0.08%)	⬆️

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[JoTurk]

Thank you, this should be done inside the bot branch here #895 also to fix the modernize issues.