Fix exponential histogram aggregation

[ocelotl]

Describe your environment

OS: (e.g, Ubuntu)
Python version: (e.g., Python 3.8.10)
SDK version: (e.g., 1.25.0)
API version: (e.g., 1.25.0)

What happened?

The aggregation of the exponential histogram with CUMULATIVE collection aggregation temporality is wrong.

Steps to Reproduce

Run this

Expected Result

Same start time for all points with CUMULATIVE collection aggregation temporality.

Actual Result

Different start time for all points with CUMULATIVE collection aggregation temporality.

Additional context

No response

Would you like to implement a fix?

None

[zhihali]

I would like to ask if this issue is related to or could potentially solve issue #3974. Both seem to deal with the StartTimeUnixNano property in the context of ExponentialHistogram metrics.

[ocelotl]

It is very likely they are related, the exponential histogram aggregation needs a complete refactoring similar to #3429