Improve performance of frames tracking

[buenaflor]

📜 Description

Note: this will be merged into v8

We can update v9 afterwards

Current implementation

• Every frame start and end create DateTime objects
• Every frame will execute the FrameTimingCallback
• The SentryDelayedFramesTracker receives the callback and then judges whether the frame is delayed or not
• Leads to unnecessary overhead since every frame triggers the callback

New implementation

• Only collect frame data if the tracking is enabled (guarded by isTrackingEnabled flag)
• Use stopwatch instead of DateTime object
• If we captured a delayed frame with the stopwatch, only then will we create datetime objects and execute the FrameTimingCallback

💡 Motivation and Context

There has been some reports of stutters or slowness when using the frames tracking.

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• 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

[codecov]

Codecov Report

Attention: Patch coverage is 95.55556% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (temp/8.14.2@2a30a8a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
flutter/lib/src/binding_wrapper.dart	93.10%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             temp/8.14.2    #2854   +/-   ##
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  Coverage               ?   92.10%           
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  Files                  ?       91           
  Lines                  ?     2963           
  Branches               ?        0           
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  Hits                   ?     2729           
  Misses                 ?      234           
  Partials               ?        0           

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