[exporters] Native Marshallers should always write SUM

[mosesn]

Problem

We found that sometimes we would export bad values from otel when the sum was 0 when we were also exporting deltas. My colleague @natasha-aleksandrova found that this was because the native histogram marshalers would omit the sum, since they were using the old serializeDouble method, instead of serializeDoubleOptional.

Solution

Update the marshallers to use serializeDoubleOptional and add a test. I confirmed that the test fails before the change, and passes after the change.

Result

The native marshalers properly export the histogram even when the sum is 0!

[linux-foundation-easycla]

• ❌ - login: @mosesn / name: Moses Nakamura . The commit (cb1462b) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (284a64f) to head (cb1462b).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8107   +/-   ##
=========================================
  Coverage     90.32%   90.32%           
  Complexity     7607     7607           
=========================================
  Files           839      839           
  Lines         22888    22888           
  Branches       2283     2283           
=========================================
  Hits          20673    20673           
  Misses         1506     1506           
  Partials        709      709           

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[jack-berg]

@mosesn can you sign the CLA? Thanks