Instead of mutating here, can we produce a new hash value? We want callers to be able to reuse the hash they've sent us after they send it to Tempo. Something like:

```ruby
converted = datapoints.map do |dp|
  {
    :t => dp[:t].iso8601(3) if dp[:t]
    :v => dp[:v] if dp[:v]
    :key => dp[:key] if dp[:key]
    :id => dp[:id] if dp[:id]
  }
end
```

I know it's a bit redundant, but it prevents mutating the callers params.