Support Render X-Request-Start nanosecond timestamps

[nateberkopec]

Render sends X-Request-Start as a whole-nanosecond epoch timestamp.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.68%. Comparing base (7d10c02) to head (dfd2b88).
⚠️ Report is 108 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2976      +/-   ##
==========================================
+ Coverage   90.13%   90.68%   +0.54%     
==========================================
  Files         132      146      +14     
  Lines        5301     5710     +409     
==========================================
+ Hits         4778     5178     +400     
- Misses        523      532       +9     

Components	Coverage Δ
sentry-ruby	97.28% <ø> (-0.01%)	⬇️
sentry-rails	55.35% <ø> (-0.15%)	⬇️
sentry-sidekiq	95.84% <ø> (+0.79%)	⬆️
sentry-resque	94.44% <ø> (ø)
sentry-delayed_job	94.68% <ø> (ø)
sentry-opentelemetry	99.56% <100.00%> (+0.25%)	⬆️

Files with missing lines	Coverage Δ
sentry-ruby/lib/sentry/rack/capture_exceptions.rb	94.25% <100.00%> (+0.50%)	⬆️

... and 40 files with indirect coverage changes

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[nateberkopec]

Hang on, I think I'm wrong about the premise.