Rate limits for multi-item envelopes are very aggressive

[Dav1dde]

In envelopes which contain multiple of some kind (e.g. N spans, N logs, N attachments), the rate limiter does not over-accept. Which means if we could fit 999 items within the rate limit, but the envelope contains 1000, we drop all of the 1000 items instead of just one or letting all of them through (over accept, what we do for metrics).