feat!: add support for crash-time attachments via hint

[jpnurmi]

Merge attachments and pass as hint to on_crash, then use the resulting hint attachments in the envelope.

Caution

BREAKING CHANGE: on_crash callbacks now have an additional sentry_hint_t *hint parameter.

Close: #2098

[cursor]

Cursor Bugbot has reviewed your changes and found 3 potential issues.

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[codecov]

Codecov Report

❌ Patch coverage is 67.08861% with 52 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.42%. Comparing base (98b9bfe) to head (cf8a5b8).

Additional details and impacted files

@@                  Coverage Diff                   @@
##           jpnurmi/feat/hints    #2112      +/-   ##
======================================================
+ Coverage               75.33%   75.42%   +0.09%     
======================================================
  Files                     103      103              
  Lines                   27939    28026      +87     
  Branches                 5103     5114      +11     
======================================================
+ Hits                    21049    21140      +91     
+ Misses                   5559     5550       -9     
- Partials                 1331     1336       +5     

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