Remove SDK's attributeset usage in stdout, add tests

[cijothomas]

AttributeSet is designed for Metric aggregation. It looks like it got accidentally used for stdout exporter. stdout already has its own AttributeSet and don't need the one from Metric module. I think AttributeSet from SDK can be made internal only, after I do another round of cleanup.

Also added some tests for Eq,Hash as we provide custom implementation. Ideally, we should test for all types, but just added for Float only as we use OrderedFloat to get Hash/Eq etc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.3%. Comparing base (348ec9e) to head (dd6b7f0).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1730     +/-   ##
=======================================
+ Coverage   71.0%   71.3%   +0.3%     
=======================================
  Files        135     136      +1     
  Lines      20751   20840     +89     
=======================================
+ Hits       14746   14879    +133     
+ Misses      6005    5961     -44     

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