Move inmemory exporter for spans to diff namespace

[cijothomas]

#2538 for traces.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.8%. Comparing base (97cf951) to head (5781174).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2544   +/-   ##
=====================================
  Coverage   77.8%   77.8%           
=====================================
  Files        122     122           
  Lines      23030   23030           
=====================================
+ Hits       17927   17931    +4     
+ Misses      5103    5099    -4     

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