Removes issue where we don't push initial blob, moves to better sync.Pool, metrics are on newer format

[element-of-surprise]

Found an issue where we would duplicate sends.

• Added test to address issue

Using sync.Pool, went to gostdlib typed version

• Cleaner and safer

Metrics on new format

• Kinda, all the metrics now with arn_sdk instead of unsupported arn-sdk now remove quotes using new format
• Weirdly, "target" which is autogenerated stays in the old one unless we go to 1.60 and use a special option, so that stays
• New stuff emits _count and _total automatically for certain metric types, so I had to deduplicate it
• This fixes the tests which I think we already broken.