Add support for `Count` and `Sum` aggregations in histogram metrics

Count and Sum fields are stored separately, and HyperDX currently errors if these aggregation functions are selected.

<img width="1483" height="597" alt="Image" src="https://github.com/user-attachments/assets/d3b1cd74-682b-4764-96e4-b0db87e6bf62" />

Ref: https://discord.com/channels/1149498480893640706/1149500035403350036/1445448370406686730