Limit to push metrics single point in time per flush

[martymarron]

Description

This PR adds the restriction to push metrics only at the most recent point in a flush period. This aims to improve the performance of pushing by eliminating redundant metrics to be pushed.
Besides, this PR conducts some code-clean-ups.

[ezh]

k6 processes its outputs once per second and that is also a default flush period in this extension. The number of k6 builtin metrics is 26 and they are collected at the rate of 50ms. In practice it means that there will be around 1000-1500 samples on average per each flush period in case of raw mapping. If custom metrics are configured, that estimate will have to be adjusted.

https://github.com/my-troubleshooting/sprint-prometheus/tree/main

[martymarron]

k6 processes its outputs once per second and that is also a default flush period in this extension. The number of k6 builtin metrics is 26 and they are collected at the rate of 50ms. In practice it means that there will be around 1000-1500 samples on average per each flush period in case of raw mapping. If custom metrics are configured, that estimate will have to be adjusted.

https://github.com/my-troubleshooting/sprint-prometheus/tree/main

Good to know. Thanks!