Adds OTelTraceIdRatioBasedSampler

[t089]

This adds a OTelTraceIdRatioBasedSampler (see Spec).

The sampler takes the last 8 bytes of the TraceID and interprets them as a single UInt64 value which is then used for the sampling decision. As long as those bytes are randomly distributed, this gives a deterministic, but random sampling decision.

• Closes Add trace-id ratio based sampler (probabilistic) #16

This also adds the Benchmark package to benchmark the implementation.

At the moment, this draft makes use of a proposed breaking change in swift-w3c-trace-context to avoid an allocation when accessing the bytes or TraceID: slashmo/swift-w3c-trace-context#18

[t089]

Please see slashmo/swift-w3c-trace-context#18 for details on this

[slashmo]

Thanks for the PR 🙏 It's a good addition to the package, thanks for also adding benchmarks 👍 I'll do a final review pass once we get the breaking change in W3C Trace Context merged. My comments so far have mostly been around formatting.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (90d63b4) to head (efb467d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
+ Coverage   99.00%   99.01%   +0.01%     
==========================================
  Files          65       68       +3     
  Lines        1800     1831      +31     
==========================================
+ Hits         1782     1813      +31     
  Misses         18       18              

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