Support custom units for custom measurements

[denrase]

📜 Description

Closes #1053

💚 How did you test it?

• Unit Tests

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing
• No breaking changes

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against 3849fbd

[denrase]

@marandaneto Do we also have to lowercase the custom measurements provided by constructor? Java does this: https://github.com/getsentry/sentry-java/blob/54cebc81e18ff2f50da062cac751681e7e4e83d4/sentry/src/test/java/io/sentry/MeasurementUnitTest.kt#L46

[github-actions]

• 🚫 The changelog entry seems to be part of an already released section ## 7.0.0.
  Consider moving the entry to the ## Unreleased section, please.

[codecov-commenter]

Codecov Report

Base: 76.27% // Head: 87.97% // Increases project coverage by +11.69% 🎉

Coverage data is based on head (3849fbd) compared to base (4432728).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@                                Coverage Diff                                 @@
##           chore/bump-min-to-flutter-3.0.0-and-dart-2.17    #1181       +/-   ##
==================================================================================
+ Coverage                                          76.27%   87.97%   +11.69%     
==================================================================================
  Files                                                 11      120      +109     
  Lines                                                333     3783     +3450     
==================================================================================
+ Hits                                                 254     3328     +3074     
- Misses                                                79      455      +376     

Impacted Files	Coverage Δ
dart/lib/src/sentry_measurement.dart	100.00% <ø> (ø)
dart/lib/src/sentry_measurement_unit.dart	100.00% <100.00%> (ø)
dart/lib/src/sentry_client.dart	93.70% <0.00%> (ø)
dart/lib/src/http_client/tracing_client.dart	80.95% <0.00%> (ø)
dart/lib/src/sentry_envelope_item.dart	97.72% <0.00%> (ø)
dart/lib/src/transport/noop_transport.dart	0.00% <0.00%> (ø)
dart/lib/src/platform/_io_platform.dart	42.85% <0.00%> (ø)
dart/lib/src/sentry_traces_sampler.dart	93.33% <0.00%> (ø)
dart/lib/src/sentry.dart	85.71% <0.00%> (ø)
dart/lib/src/sentry_transaction_context.dart	95.23% <0.00%> (ø)
... and 100 more

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[marandaneto]

@marandaneto Do we also have to lowercase the custom measurements provided by constructor? Java does this: getsentry/sentry-java@54cebc8/sentry/src/test/java/io/sentry/MeasurementUnitTest.kt#L46

Looking at https://develop.sentry.dev/sdk/event-payloads/transaction/ I don't see anything in the spec.
Maybe @romtsn can tell us if its written somewhere or the reasons?

[romtsn]

Maybe @romtsn can tell us if its written somewhere or the reasons?

No specific reason, we just did not special-case it and used the same method apiName which lowercases the value. But looking at relay, they also lowercase it anyway, so I guess it doesn't matter what we send

[marandaneto]

Left a comment https://github.com/getsentry/sentry-dart/pull/1181/files#r1047071003 otherwise LGTM