Add golangci-lint and coverage reporting to CI

[Darkroom4364]

Summary

• Add golangci-lint job and coverage reporting to CI workflow
• Fix UDP DNS queries ignoring configured timeout (use dns.Client instead of dns.Exchange)

Test plan

• CI lint job passes
• Coverage report appears in test job output
• UDP DNS queries respect --timeout flag

[Darkroom4364]

Review — Request Changes

CI additions (lint job, coverage reporting) are correct and useful.

Issues:

• ~15 unrelated code changes bundled with the CI change (NO_COLOR, UTF-8 validation, error surfacing, batch refactor, skip counting, timeout validation, etc.). Split into CI-only vs. code/logic PRs.
• DoH timeout is plumbed through but the UDP dns.Exchange path still ignores it — should use a dns.Client with timeout set for consistency.
• Corruption threshold: when len(corrupted) <= 6, no byte gets flipped — silent false negative. Worth a guard or comment.

[Darkroom4364]

Linting failing