Configurable limit to the number of attributes that can be added to a span

[kstenerud]

Goal

This is the second half to #314

[github-actions]

BugsnagPerformance.framework binary size increased by 856 bytes from 481,064 to 481,920

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.5%    +584  +0.5%    +584    __TEXT,__text
  +0.4%    +456  +0.4%    +456    String Table
  +0.4%    +384  +0.4%    +384    Symbol Table
  +2.9%    +209  +2.9%    +209    __TEXT,__cstring
  +1.3%    +192  +1.3%    +192    __DATA,__objc_const
  +1.4%    +181  +1.4%    +181    __TEXT,__objc_methname
  +0.7%     +80  +0.7%     +80    __TEXT,__gcc_except_tab
  +0.4%     +32  +0.4%     +32    __DATA_CONST,__cfstring
  +0.3%     +32  +0.3%     +32    __TEXT,__objc_stubs
  +0.3%     +16  +0.3%     +16    __TEXT,__unwind_info
  +0.7%      +8  +0.7%      +8    Function Start Addresses
  +0.9%      +8  +0.9%      +8    Rebase Info
  +2.6%      +8  +2.6%      +8    __DATA,__objc_ivar
  +0.3%      +8  +0.3%      +8    __DATA,__objc_selrefs
  +0.1%      +3  +0.1%      +3    __TEXT,__objc_methtype
  -1.2%     -32  -1.2%     -32    [__DATA_CONST]
  -1.7%    -208  -1.7%    -208    [__DATA]
  [ = ]       0  -8.2%    -856    [__LINKEDIT]
  -2.6% -1.08Ki  -2.6% -1.08Ki    [__TEXT]
  +0.2%    +856  [ = ]       0    TOTAL

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