Rate limiting on compressed data

Right now rate limiting is done on uncompressed data which forces us to spend some CPU cycles even if we reject the payload.

We have a consensus that we should most likely do this on compressed data instead and reject it as soon as possible.

Start by locating the rate-limiting path and the compressed-payload handling in the Pyroscope codebase. Trace where payloads are currently decompressed relative to rejection, then identify the existing tests covering rate limiting or compressed data. Done means rejected payloads are stopped using compressed data before unnecessary decompression, with relevant behavior covered by tests.

Written by the indexing model from the issue text.