Add test based on the Jaeger spec

[Grunet]

Adds a specific test based on the spec example, since I tried at least twice at the logic and missed both times until @saktib fixed it all up...

Also fixes up some flakiness I noticed after running the tests a few times, like here https://github.com/open-telemetry/opentelemetry-php/runs/5763933166?check_suite_focus=true

[codecov]

Codecov Report

Merging #645 (9088731) into main (178cc9e) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #645   +/-   ##
=========================================
  Coverage     84.45%   84.45%           
  Complexity     1141     1141           
=========================================
  Files           127      127           
  Lines          2766     2766           
=========================================
  Hits           2336     2336           
  Misses          430      430           

Flag	Coverage Δ
7.4	84.40% <ø> (ø)
8.0	84.45% <ø> (ø)
8.1	84.45% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 178cc9e...9088731. Read the comment docs.