feat: track DNS request source in metrics and logs

[rm-hull]

Introduce DNSSource and RequestContext to differentiate between UDP, TCP, and DoT requests throughout the dispatching lifecycle.

• Update DNSDispatcher to accept the request source.
• Enhance dns_request_count metric with a source label.
• Consolidate logging context to include source and metadata.

[github-actions]

	Tests	Passed ✅	Skipped	Failed
JUnit Test Report	28 ran	28 passed	0 skipped	0 failed

Test	Result
JUnit Test Report
com/rm-hull/dot-block/internal/blocklist.TestIsBlocked_ApexDomain_PublicSuffix	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_HandleDNSRequest_Allowed	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_HandleDNSRequest_Blocked	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_HandleDNSRequest_MultipleQuestions	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_HandleDNSRequest_CacheHit	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_ResolveUpstream_BadRCode	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestNewDNSDispatcher_NegativeCacheTtlFloor	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_QueryLogging/Logging_at_INFO_level_(should_not_contain_debug_logs)	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_QueryLogging/Logging_at_DEBUG_level	✅ passed
com/rm-hull/dot-block/internal/forwarder.TestDNSDispatcher_QueryLogging	✅ passed
com/rm-hull/dot-block/internal/metrics.TestNewSpaceSaverStatsCallback/eviction_case	✅ passed
com/rm-hull/dot-block/internal/metrics.TestNewSpaceSaverStatsCallback/topK_smaller_than_items	✅ passed
com/rm-hull/dot-block/internal/metrics.TestNewSpaceSaverStatsCallback/empty_space_saver	✅ passed
com/rm-hull/dot-block/internal/metrics.TestNewSpaceSaverStatsCallback	✅ passed
com/rm-hull/dot-block/internal/metrics.TestNewSpaceSaver	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverAdd/Case3_ReplacementDetails	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverAdd	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverTopN/TopN_WithReplacements	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverTopN	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverConcurrency	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyInitialization	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyAfterFirstAdd	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyAddingItemsWithSameCount	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyAfterIncrementingMinKeyItem	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyAfterReplacement	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching/MinKeyInvalidationAndRecomputation	✅ passed
com/rm-hull/dot-block/internal/metrics.TestSpaceSaverMinKeyCaching	✅ passed
com/rm-hull/dot-block/internal/mobileconfig.TestHandler	✅ passed

• View JUnit Test Report

[gemini-code-assist]

Code Review

This pull request refactors the DNS request handling to track and report the source of DNS requests (UDP, TCP, or DoT) in metrics and logs. It introduces a DNSSource type and a RequestContext struct to pass contextual information through the dispatcher. The review feedback suggests several improvements: removing the unused StartTime field from RequestContext, and skipping both the geolocation lookup and client count updates when the client IP address is resolved as "unknown" to avoid redundant operations and duplicate warning logs.

[coveralls]

Coverage Report for CI Build 26707628692

Coverage increased (+0.2%) to 39.922%

Details

• Coverage increased (+0.2%) from the base build.
• Patch coverage: 19 uncovered changes across 2 files (61 of 80 lines covered, 76.25%).
• 1 coverage regression across 1 file.

Uncovered Changes

File	Changed	Covered	%
internal/forwarder/dispatcher.go	75	59	78.67%
internal/app.go	3	0	0.0%
Total (3 files)	80	61	76.25%

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
internal/forwarder/dispatcher.go	1	84.26%

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Coverage Stats

Relevant Lines:	1280
Covered Lines:	511
Line Coverage:	39.92%
Coverage Strength:	0.43 hits per line

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💛 - Coveralls