* Optimize fast path for /api/v1/import when importing numeric values
* Move the docs about the change from features to bugfixes at docs/CHANGELOG.md
* Update tests at lib/protoparser/vmimport
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3161
* app/vmselect: properly work when export import json from `api/v1/{export, import}` API
* app/vmselect: update convert function
* app/vmselect: export null if `math.IsNaN(v)`
* app/vmselect: get float from json
* lib/protoparser: add test
* docs: add change log
* lib/protoparser: make export import api compatible
* Export "null" in jsonl instead of NaN
The NaN appeared because of staleness markers that were added for compatibility. I think it's better to use json `null`, implemented here.
Also maybe it also makes sense to add a flag like `?skip-staleness-markers=true` to `/export`, to skip nulls at all?
* Update app/vmselect/prometheus/export.qtpl
* app/vmselect/prometheus/export.qtpl.go: `make quicktemplate-gen`
* docs/CHANGELOG.md: document the change
Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>