impr: Remove char limit of 8192 for SentryMessage

[philipphofmann]

📜 Description

Let Relay truncate the max char length. The benefit is that users see that the message was truncated.

💡 Motivation and Context

Fixes GH-5004

💚 How did you test it?

Unit tests

📝 Checklist

You have to check all boxes before merging:

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.694%. Comparing base (fd1c994) to head (1af6eda).
Report is 6 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #5005       +/-   ##
=============================================
+ Coverage   92.608%   92.694%   +0.086%     
=============================================
  Files          672       672               
  Lines        82199     82199               
  Branches     28819     29840     +1021     
=============================================
+ Hits         76123     76194       +71     
+ Misses        5983      5906       -77     
- Partials        93        99        +6     

Files with missing lines	Coverage Δ
Sources/Sentry/SentryMessage.m	100.000% <100.000%> (ø)
...ests/SentryTests/Protocol/SentryMessageTests.swift	100.000% <100.000%> (ø)

... and 31 files with indirect coverage changes

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[philprime]

LGTM