Fix issues with stopping Vernier

[solnic]

This ensures that we rely on status returned from Vernier.start_profile when setting profiler's @started value and also now Sentry::Vernier::Profiler#stop will fail gracefully when for whatever reason stopping crashed.

Fixes #2425

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.67%. Comparing base (499cbac) to head (760804d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2429   +/-   ##
=======================================
  Coverage   98.67%   98.67%           
=======================================
  Files         220      220           
  Lines       14450    14462   +12     
=======================================
+ Hits        14258    14270   +12     
  Misses        192      192           

Components	Coverage Δ
sentry-ruby	99.01% <100.00%> (-0.01%)	⬇️
sentry-rails	97.34% <ø> (ø)
sentry-sidekiq	97.07% <ø> (ø)
sentry-resque	97.11% <ø> (+0.32%)	⬆️
sentry-delayed_job	98.92% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (ø)

Files with missing lines	Coverage Δ
sentry-ruby/lib/sentry/vernier/profiler.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/vernier/profiler_spec.rb	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes