Fix: Capture Callback Exceptions

[denrase]

📜 Description

Capture and log exceptions thrown in callbacks provided users.

💡 Motivation and Context

All exceptions should be caught and handled gracefully.

Relates to getsentry/team-mobile#21

💚 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

[codecov-commenter]

Codecov Report

Base: 89.47% // Head: 91.14% // Increases project coverage by +1.66% 🎉

Coverage data is based on head (1162126) compared to base (d90ceb9).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #990      +/-   ##
==========================================
+ Coverage   89.47%   91.14%   +1.66%     
==========================================
  Files         106        9      -97     
  Lines        3326      192    -3134     
==========================================
- Hits         2976      175    -2801     
+ Misses        350       17     -333     

Impacted Files	Coverage Δ
dart/lib/src/hub.dart
dart/lib/src/scope.dart
dart/lib/src/sentry.dart
dart/lib/src/transport/rate_limit.dart
dart/lib/src/protocol/dsn.dart
dart/lib/src/protocol/sentry_stack_frame.dart
dart/lib/src/transport/encode.dart
dart/lib/src/sentry_sampling_context.dart
dart/lib/src/protocol/sentry_span.dart
...t/lib/src/sentry_attachment/sentry_attachment.dart
... and 87 more

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[marandaneto]

@denrase there's one broken test.