Replace internal access to traceId property with traceIdHi and traceIdLo

[yousif-bugsnag]

Goal

Methods/properties that return a struct (such as traceId in BugsnagPerformanceSpanContext) cannot be proxied in the CrossTalk API and would crash if accessed through a proxy object.

This PR adds two new properties for traceIDHi and traceIdLo to BugsnagPerformanceSpanContext and updates internal code to never access traceId on a span or span context and use these new properties instead.

Testing

Relied on existing tests

[github-actions]

BugsnagPerformance.framework binary size increased by 320 bytes from 524,168 to 524,488

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [ = ]       0 +13e3% +15.7Ki    [__LINKEDIT]
  +0.2%    +192  +0.2%    +192    Symbol Table
  +0.1%    +128  +0.1%    +128    String Table
  +0.1%     +84  +0.1%     +84    __TEXT,__text
  +0.4%     +80  +0.4%     +80    __DATA,__objc_const
  +0.5%     +64  +0.5%     +64    __TEXT,__objc_stubs
  +0.2%     +27  +0.2%     +27    __TEXT,__objc_methname
  +0.5%     +16  +0.5%     +16    __DATA,__objc_selrefs
  +0.2%      +8  +0.2%      +8    __TEXT,__unwind_info
  -0.1%      -8  -0.1%      -8    __TEXT,__gcc_except_tab
  -1.6%     -96  -1.6%     -96    [__DATA]
  -0.4%    -175  -0.4%    -175    [__TEXT]
  +0.1%    +320  +3.1% +16.0Ki    TOTAL

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