[PLAT-8749] Trim breadcrumbs in oversized payloads

[nickdowell]

Goal

Reduce number of errors being lost due to exceeding Bugsnag's size limit.

Design

Removes and / or trims (removing their message and metadata) breadcrumbs until the event payload fits within the size limit.

Changeset

Adds trimming method -[BugsnagEvent trimBreadcrumbs:] which accepts a number of bytes to trim.

Updates BSGEventUploadOperation to call trimBreadcrumbs: if the payload exceeds the size limit.

Testing

Adds unit test cases and an E2E scenario to verify behaviour.

[github-actions]

Bugsnag.framework binary size increased by 136 bytes from 771,504 to 771,640

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.6% +1.54Ki  +0.6% +1.54Ki    __TEXT,__text
  +4.5%    +156  +4.5%    +156    __TEXT,__gcc_except_tab
  +0.6%    +128  +0.6%    +128    __DATA,__cfstring
  +0.5%     +99  +0.5%     +99    __TEXT,__cstring
  +0.3%     +81  +0.3%     +81    __TEXT,__objc_methname
  +0.1%     +80  +0.1%     +80    Symbol Table
  +0.0%     +48  +0.0%     +48    String Table
  +0.5%     +32  +0.5%     +32    __DATA,__objc_selrefs
  +0.0%     +24  +0.0%     +24    __DATA,__objc_const
  +0.4%      +8  +0.4%      +8    Function Start Addresses
  [ = ]       0  -0.9%    -136    [__LINKEDIT]
  -1.6%    -184  -9.2%    -184    [__DATA]
 -12.5% -1.87Ki -12.5% -1.87Ki    [__TEXT]
  +0.0%    +136  [ = ]       0    TOTAL

Generated by 🚫 Danger