Skip request-body compression for small payloads

[vdusek]

The Python API client compresses every request body regardless of size (see #927). For small payloads the compression overhead isn't worth it.

The JS client skips compression when the body is below 1024 B. We should align the Python client with that behavior and only compress bodies at or above the threshold.

Context: #927 (comment)

[Pijukatel]

Maybe it is also a good time to think (make some benchmarks) whether it should be done the other way around and turn it on in JS for all payloads as well.