Avoid causing NoMethodError for Sentry.* calls when the SDK is not inited

[st0012]

Closes #1706

[codecov-commenter]

Codecov Report

Merging #1713 (f4dee80) into master (42afb25) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1713      +/-   ##
==========================================
+ Coverage   98.42%   98.44%   +0.02%     
==========================================
  Files         139      140       +1     
  Lines        7944     7990      +46     
==========================================
+ Hits         7819     7866      +47     
+ Misses        125      124       -1     

Impacted Files	Coverage Δ
sentry-rails/spec/support/test_rails_app/app.rb	97.77% <100.00%> (+0.01%)	⬆️
sentry-ruby/lib/sentry-ruby.rb	95.45% <100.00%> (+1.11%)	⬆️
sentry-ruby/spec/initialization_check_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/breadcrumb.rb	100.00% <0.00%> (+3.70%)	⬆️

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[sl0thentr0py]

thx :)

[lewispb]

This PR looks good as-is but I was wondering if it was possible to avoid the explicit return unless initialized? calls everywhere.

One idea I had to do that would be to append something like this to sentry-ruby.rb (not tested):

unless Sentry.initialized?
  klass_methods = Sentry.methods(false)
  Sentry.singleton_class.prepend(Module.new do
    klass_methods.each do |method_name|
      define_method(method_name) do
        nil
      end
    end
  end)
end

That way it'd automatically cover future changes too.

[st0012]

@lewispb Yeah I've thought about that but I didn't think it's a good idea because:

1. The interfaces are pretty static. We haven't introduced any new method for months. So the ease of adding new APIs is not the most important thing here.
2. Whichever meta-programming route we take, it won't be very expressive about its intention.
3. It's more common that users/maintainers debug or investigate individual API methods than examining sentry-ruby.rb altogether. So I think explicitly stating return unless initialized? in every method makes them more understandable in most cases.

[lewispb]

@st0012 those are all good points 👍 thanks for explaining your thinking here.

[st0012]

@lewispb np, thanks for the advice too. I sincerely appreciate that you check my code and provide suggestions from time to time!