[WIP] ref!: sentry_value-based attachments

[jpnurmi]

Warning

WIP    🚧🔨⏳⛔

Caution

BREAKING CHANGE

Attachment setters now accept sentry_value_t. Attach helpers return sentry_uuid_t instead of sentry_attachment_t *, and removal takes an attachment UUID.

Scope data is moving to fine-grained read/write locking to allow concurrent readers. A read-locked getter cannot safely return a borrowed sentry_attachment_t pointer because a writer may remove and free the attachment as soon as the read lock is released.

Represent attachments and attachment collections as refcounted sentry_value_t objects. A getter can retain the value under the read lock and return an owned reference that remains valid after unlocking.

Configure attachments before insertion and freeze them once added. Use UUIDs for removal, and retain byte values while envelopes borrow their payload to avoid copying attachment data.

Resolves: #1945

[github-actions]

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Codecov Report

❌ Patch coverage is 71.84751% with 192 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.27%. Comparing base (e5d9bca) to head (77576ea).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           jpnurmi/fix/unwinder-arm32-ip    #1974      +/-   ##
=================================================================
+ Coverage                          74.25%   74.27%   +0.01%     
=================================================================
  Files                                104      104              
  Lines                              25365    25616     +251     
  Branches                            4535     4566      +31     
=================================================================
+ Hits                               18835    19026     +191     
- Misses                              5232     5302      +70     
+ Partials                            1298     1288      -10     

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