refactor(export): add sentry transformer to sentry_dio exports

[tsinis]

📜 Description

Exports the SentryTransformer class from the sentry_dio package (src/sentry_transformer.dart).

This makes the transformer class available for users to import and utilize directly if needed for custom Dio client transformer configurations.

💡 Motivation and Context

When integrating Sentry with Dio, the addSentry() method overwrites Dio's default transformer with Sentry's own wrapper - SentryTransformer. However, in some cases, there are performance benefits of Dio's BackgroundTransformer (that could be passed to the SentryTransformer's transformer parameter), which processes large payloads (>50KB) in separate isolates. But since SentryTransformer is not exported, there is no easy way to do it.

💚 How did you test it?

• Verified that the package (sentry_dio) compiles successfully with the added export.
• Manually confirmed in a sample project that SentryTransformer can be successfully imported via import 'package:sentry_dio/sentry_dio.dart';.
• The need for this change was identified through performance analysis in an application experiencing UI freezes when decoding large (multi-MB) JSON responses after integrating sentry_dio.

📝 Checklist

• I reviewed submitted code
• Tests are not needed for exports
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

Consider adding documentation explaining what addSentry() does under the hood and how it could be customized.

[ueman]

This is actually not needed, since you should configure dio first, and as a last step call addSentry(). Since Sentry does not override any user configuratioon, it then uses whatever transformer you configured dio to use.

See this

sentry-dart/dio/lib/src/sentry_dio_extension.dart

Lines 94 to 97 in 18b7c08

	httpClientAdapter = SentryDioClientAdapter(
	client: httpClientAdapter,
	hub: hub,
	);

and this

sentry-dart/dio/lib/src/sentry_dio_extension.dart

Lines 100 to 103 in 18b7c08

	transformer = SentryTransformer(
	transformer: transformer,
	hub: hub,
	);

This also ensures that integrating Sentry with dio is as seamless as possible, since it's just adding or removing the addSentry() call.

So here's how you should use it:

final dio = Dio();
dio.transformer = ...;
dio.httpClientAdapter = ...;
dio.addSentry(); // Dio is used with whatever transformer is configured two lines above AND also with Sentry

Disclaimer: I'm not a Sentry employe, but I wrote the Sentry dio integration and was a former dio maintainer

[tsinis]

Hey @ueman I see, yes - make sense, but this is still not that obvious, I will provide documentation update in a separate PR, thanks!

[ueman]

It's already stated in the docs here:

sentry-dart/dio/lib/src/sentry_dio_extension.dart

Lines 17 to 18 in 18b7c08

	/// This must be the last initialization step of the [Dio] setup, otherwise
	/// your configuration of Dio might overwrite the Sentry configuration.

But yeah, I guess a more exhaustive explanation can not hurt