fix: Maintain client in crashpad state

[supervacuus]

This PR is related to this issue: #900 (comment).

The crashpad client is stateful (on macOS, it contains the send right to the exception port), and it might be a good idea to keep the client instance for the life cycle of the Native SDK. This also fixes part of the issue (terminating one crashpad_handler kills the other). I don't see any downside to this, although having a second client will almost always overwrite a previously initialized one.

[codecov]

Codecov Report

Merging #910 (7f98f9e) into master (9901c01) will increase coverage by 0.11%.
The diff coverage is 80.00%.

❗ Current head 7f98f9e differs from pull request most recent head f07b3e3. Consider uploading reports for the commit f07b3e3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #910      +/-   ##
==========================================
+ Coverage   82.59%   82.71%   +0.11%     
==========================================
  Files          53       53              
  Lines        7372     7376       +4     
  Branches     1185     1185              
==========================================
+ Hits         6089     6101      +12     
+ Misses       1175     1167       -8     
  Partials      108      108              

[markushi]

LGTM!