Previously, metricMetadata was not properly reset during parsing of
metrics. It could result into `Unit` suffix to be added from previously
parsed metric into next metric without Unit field.
For example, metric `http_request` with `Unit` `seconds` will be
converted into `http_request_seconds` and `Unit` field hold `seconds`.
Next parsed metric `cpu_usage_ratio` has no `Unit` and it will get
previous `seconds` `Unit` -> `cpu_usage_ratio_seconds`.
This commit adds metricMetadata reset call before parsing of next
metric.
Bug was introduced at 293d80910c
Fixes https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10889
89c0b1c1aa