fix: Clone scope.Context in multiple places to avoid concurrent reads/writes

[tonyo]

Fixes #570

Here we introduce cloneContext that should be used in multiple places to avoid issues like in #570.

Note: cloneContext does not do a deep copy of Context values (which are of type interface{}), so there are cases where it's still possible to catch panics if you do weird things with Context values. But this, I believe, is out of scope of the SDK responsibility.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.05 ⚠️

Comparison is base (eec094e) 79.72% compared to head (cb73fed) 79.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #638      +/-   ##
==========================================
- Coverage   79.72%   79.67%   -0.05%     
==========================================
  Files          38       38              
  Lines        3896     3902       +6     
==========================================
+ Hits         3106     3109       +3     
- Misses        681      683       +2     
- Partials      109      110       +1     

Impacted Files	Coverage Δ
scope.go	91.12% <100.00%> (+0.21%)	⬆️
tracing.go	89.43% <100.00%> (ø)

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.