promql, tsdb (histograms): Do not re-use spans between histograms
When multiple points exist with the same native histogram schemas they
share their spans.
This causes a problem when a native histogram (NH) schema is modified (for example, during
a Sum) then the other NH's with the same spans are also modified. As such,
we should create a new Span for each NH. This will ensure NH's interfaces
are safe to use without considering the effect on other histograms.
At the moment this doesn't present itself as a problem because in all
aggregations and functions operating on native histograms they are copied
by the promql query engine first.
Signed-off-by: Joshua Hesketh <josh@nitrotech.org>
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Signed-off-by: Joshua Hesketh <josh@nitrotech.org>