Add stackprof based profiler

[sl0thentr0py]

resolves #2013

Usage

• Add stackprof to Gemfile as a peer dependency

Sentry.init do |config|
  config.traces_sample_rate = 1.0
  config.profiles_sample_rate = 1.0
  config.release = "release"
end

[codecov]

Codecov Report

Patch coverage: 99.22% and project coverage change: +0.01 🎉

Comparison is base (bad263c) 98.58% compared to head (d6ba93f) 98.60%.

❗ Current head d6ba93f differs from pull request most recent head ec0a24f. Consider uploading reports for the commit ec0a24f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2024      +/-   ##
==========================================
+ Coverage   98.58%   98.60%   +0.01%     
==========================================
  Files         157      159       +2     
  Lines       10127    10506     +379     
==========================================
+ Hits         9984    10359     +375     
- Misses        143      147       +4     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry/scope.rb	100.00% <ø> (ø)
sentry-ruby/lib/sentry/profiler.rb	97.27% <97.27%> (ø)
sentry-ruby/lib/sentry/configuration.rb	98.62% <100.00%> (+0.04%)	⬆️
sentry-ruby/lib/sentry/envelope.rb	97.95% <100.00%> (ø)
sentry-ruby/lib/sentry/hub.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/transaction.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/transaction_event.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/transport.rb	99.05% <100.00%> (+0.01%)	⬆️
sentry-ruby/spec/sentry/configuration_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/profiler_spec.rb	100.00% <100.00%> (ø)
... and 4 more

... and 1 file with indirect coverage changes

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[sl0thentr0py]

hey @st0012 @Zylphrex I believe this is shippable now, I'll write up a PR description and documentation etc next week, feel free to take a look and start reviewing!

[sl0thentr0py]

alright I believe I covered all the comments, @st0012

[st0012]

IMO using null-object pattern here is an overkill.

Give that:

1. All public profiler APIs no-op if not @sampled
2. @sampled will never be true unless @profiling_enabled

Can we do this instead?

1. Define a single Profiler class
2. In Profiler's constructor, we use:

@profiling_enabled = defined?(StackProf) && configuration.profiling_enabled?

Alternatively, I think just early returning the initialize method may also work.

[st0012]

Amazing 🎉

[sl0thentr0py]

ok I did one more round of sanity check testing, looks ok. I'm merging!