feat: enable brotli request compression by default

[vdusek]

Enables brotli compression as the default for all SDK/client ↔ platform communication.

apify-client v3 defaults to gzip, so enabling brotli takes two parts:

• Dependency: pull in the apify-client[brotli] extra so the brotli backend is installed. apify-client v3.1 (which adds request body compression) isn't released yet, so this temporarily pins the latest beta that already ships the extra (apify-client[brotli]>=3.0.7b1). A TODO in pyproject.toml tracks switching to >=3.1.0 once v3.1 is out.
• Code: both places where the SDK constructs an ApifyClientAsync (Actor.new_client and the storage-client factory _create_api_client) now pass compression='brotli'. Since the SDK hard-depends on apify-client[brotli], the brotli backend is always installed, so brotli is passed directly.

Tests: a wire-level test drives a real request through an SDK-created client against a local HTTP server and asserts the body goes out with Content-Encoding: br and round-trips back through brotli.decompress. It's parametrized over both client-creation paths (_create_api_client and Actor.new_client).

Closes #1045

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.87%. Comparing base (573e3a3) to head (33271d5).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1052      +/-   ##
==========================================
+ Coverage   91.77%   91.87%   +0.10%     
==========================================
  Files          50       50              
  Lines        3222     3225       +3     
==========================================
+ Hits         2957     2963       +6     
+ Misses        265      262       -3     

Flag	Coverage Δ
e2e	35.56% <ø> (-0.01%)	⬇️
integration	57.33% <ø> (-0.03%)	⬇️
unit	83.22% <ø> (+0.10%)	⬆️

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