perf: optimise stall tracking

[matinzd]

📢 Type of change

• Bugfix
• New feature
• Enhancement
• Refactoring

📜 Description

(WIP)

UPDATE 1:

This pull request optimizes the stall tracking integration by simplifying how the longestStallTime is tracked. Previously, the longestStallTime was tracked for each transaction (root span) individually within the statsByRootSpan map. This approach involved iterating over all transactions during each stall detection, which could be inefficient, especially with a large number of transactions.

💡 Motivation and Context

This pull request enhances performance and potentially resolves critical animation flickering issues on iOS devices as reported in Issue #3987. The changes may lead to a more efficient event loop, and smoother animations.

💚 How did you test it?

Running tests that have been in place before. Let me know if we need more test cases.

📝 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
• All tests passing
• No breaking changes

🔮 Next steps

[matinzd]

The issue is fixed in v6 with the new stall tracking integration:

#3997