fix stream transport factory creation

[brettmc]

when creating a stream from an endpoint string, the factory wasn't returning the stream. fix and add tests.

[codecov]

Codecov Report

Merging #882 (6caef34) into main (0ce2fda) will increase coverage by 0.35%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #882      +/-   ##
============================================
+ Coverage     81.21%   81.56%   +0.35%     
  Complexity     2008     2008              
============================================
  Files           264      264              
  Lines          5212     5219       +7     
============================================
+ Hits           4233     4257      +24     
+ Misses          979      962      -17     

Flag	Coverage Δ
7.4	81.05% <100.00%> (+0.35%)	⬆️
8.0	81.55% <100.00%> (+0.35%)	⬆️
8.1	81.69% <100.00%> (+0.35%)	⬆️

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Impacted Files	Coverage Δ
...DK/Common/Export/Stream/StreamTransportFactory.php	81.81% <100.00%> (+81.81%)	⬆️
src/SDK/Trace/SpanProcessor/BatchSpanProcessor.php	100.00% <100.00%> (ø)
...rc/SDK/Trace/SpanProcessor/SimpleSpanProcessor.php	100.00% <100.00%> (ø)

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