feat(tracer): independent trace cancellation and per-operation hop options

[dweekly]

Summary

Implements the first phase of the Cache and Network-Transition Lifecycle proposal from docs/CACHE-AND-TRANSITION-LIFECYCLE.md:

• cancelActiveTraces(): Decouples active trace cancellation from cache invalidation. Snapshots and cancels in-flight trace handles while preserving cached rDNS, public IP, and ASN data. Traces registered after cancellation begins remain tracked for subsequent operations.
• TraceOptions: Additive per-operation configuration struct providing maxHops override (validated against 1...255), available via trace(to:options:) and traceClassified(to:vpnContext:resolver:options:).
• Source and binary compatibility: Retains exact existing trace(to:) and traceClassified(to:vpnContext:resolver:) entry points so downstream callers and DocC symbol links remain fully backward compatible.
• Conservative composition: networkChanged() delegates directly to cancelActiveTraces() while preserving its full cache invalidation contract.

Testing

• Added TraceLifecycleTests covering:
  • cancelActiveTraces() cancelling active traces without wiping rDNS or cached public IP, and confirming networkChanged() still clears both.
  • TraceOptions maxHops bounding trace hops.
  • TraceOptions out-of-range validation throwing TracerouteError.invalidConfiguration.
• Ran full test suite (all 325 tests passing).
• Validated DocC builds warning-clean with --warnings-as-errors.
• Validated swift format lint --strict.