perf: Skip request-body compression for small payloads

[vdusek]

Until now the Python client compressed every request body regardless of size. It now skips compression below 1024 B.

Closes #934

Why 1024 B

• Parity with the JS client. It uses the same threshold, the same operator (>=), and the same byte-based measurement (MIN_COMPRESS_BYTES in apify-client-js/src/utils.ts), so both clients now put identical bytes on the wire.
• Small bodies grow. run.charge 40 B to 59 B, kvs.set_record 27 B to 45 B, single-item dataset.push_items 10 B to 30 B. gzip breaks even only at ~88 B of realistic JSON, and high-entropy bodies such as binary key-value store records inflate at any size, by ~23 B for gzip and ~4 B for brotli.
• No packet is saved below ~1 KB, and removing a packet is the only thing that buys latency. With ~500 B of request headers on a 1400 B MSS:

Raw body	gzipped	Segments raw to gzip	Packet saved?
786 B	344 B	1 to 1	no
1071 B	447 B	2 to 1	yes
8250 B	2958 B	7 to 3	yes

Compressing everything instead, the reverse direction raised in the issue, doesn't pay off. Over 1200 realistic bodies it inflates 749 of them while total bytes move only from −62.1% to −63.8%, and that gain sits entirely in the 512–1024 B band where no packet is saved anyway. At 1024 B nothing inflates.

Changes

• MIN_COMPRESSION_SIZE = 1024. _prepare_request_call compresses only at or above it, measured on the encoded bytes so a multibyte str is judged correctly.
• A caller-supplied Content-Encoding is now dropped on a skipped body, where it would otherwise survive and mislabel an uncompressed payload.
• The async client skips the asyncio.to_thread hop for any body it won't compress, the hop costing 36–68 µs against 5–12 µs of compression. _is_body_worth_compressing sits next to the rule it mirrors so the two can't drift apart. A json= body still hops, its size being unknown until serialized.
• Docs: new "Minimum body size" section. The page claimed the client compresses every request body.

Verification

Against the live API, 8 value shapes round-trip byte-identical with and without compression, small uncompressed bodies are accepted by dataset.push_items, rq.add_request, rq.batch_add_requests, dataset.update, schedules().create, schedule.update, and webhooks().create, and latency is unchanged.

Tests that compressed tiny bodies were passing vacuously. They now cover the 0/1/1023/1024/1025 boundary for both gzip and brotli, the byte-vs-character threshold, the dropped header, and the thread-hop decisions. test_run_charge's compression axis was the suite's only end-to-end compression coverage and had gone vacuous on its 39-byte body, so it's replaced by a test asserting an above-threshold body reaches the server compressed under the configured algorithm.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.71%. Comparing base (808bdde) to head (d112162).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #988      +/-   ##
==========================================
- Coverage   94.72%   94.71%   -0.01%     
==========================================
  Files          58       58              
  Lines        5323     5332       +9     
==========================================
+ Hits         5042     5050       +8     
- Misses        281      282       +1     

Flag	Coverage Δ
integration	92.06% <100.00%> (-0.40%)	⬇️
unit	84.45% <100.00%> (+0.21%)	⬆️

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[Mantisus]

LGTM