test(makernote): add integration tests for MakerNote detection (#15)

[rpuneet]

Summary

• Add comprehensive integration tests for MakerNote registry detection
• Tests verify detection for all 4 supported manufacturers
• Includes benchmarks for performance validation

Test Coverage

Test	Description
TestMakerNoteRegistryDetection	Detection tests for Nikon, Sony, Fujifilm, Canon
TestMakerNoteDetectionOrder	Priority verification (specific headers before Canon fallback)
TestMakerNoteMalformedHeaders	Graceful handling of invalid data
TestMakerNoteBoundaryConditions	Edge cases (max entries, min offsets)
TestMakerNoteConcurrentDetection	Thread safety verification
TestMakerNoteRealFile	Real file parsing (skipped if testdata unavailable)

Benchmarks

BenchmarkMakerNoteDetect_Nikon      346.9 ns/op    64 B/op    1 allocs/op
BenchmarkMakerNoteDetect_Sony       362.6 ns/op    64 B/op    1 allocs/op
BenchmarkMakerNoteDetect_Fujifilm   589.0 ns/op    64 B/op    1 allocs/op
BenchmarkMakerNoteDetect_Canon      484.2 ns/op    64 B/op    1 allocs/op
BenchmarkMakerNoteDetect_Unknown    279.8 ns/op     0 B/op    0 allocs/op

Test plan

• All existing tests pass
• New integration tests pass
• Benchmarks run successfully
• Verify with make build and CLI testing

Partial work on #15 - remaining items: fuzz tests, per-manufacturer parse benchmarks

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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