Phase 11: Add fuzzing targets

[rpmoore]

Roadmap step 92 from docs/steps.md.

Scope

Add fuzzing targets.

Details

Fuzz DNS parser and blocklist parser with the invariant that arbitrary input returns a parsed result or structured error, never a panic.

References

• docs/steps.md Phase 11, step 92
• docs/plan/01-dns-protocol.md#tests
• docs/plan/07-operations-testing.md#test-strategy
• docs/plan/08-implementation-roadmap.md#milestone-11-tcp-and-operational-hardening