Potential metrics loss under load

[khvn26]

During https://github.com/Flagsmith/pulumi/issues/147 we spotted a data discrepancy in route metrics during stress tests.

This graph gives a hint that something might be off with prometheus-python itself:

[emyller]

@khvn26 Do you think this is still relevant?

[khvn26]

I think it is, because we haven't confirmed this particular issue is gone (perhaps we even observed it after your changes?)