Add GeeTest v3 support (v1.1.0)

[capskip]

Adds GeeTest v3 (slide) solving to the Python SDK, matching the GeeTest v3 API docs.

What's new

result = solver.geetest(
    gt="81388ea1fc187e0c335c0a8907ff2625",
    challenge="7cf6a8b1a2c34d5e6f7089abcdef0123",
    url="https://example.com/login",
)

result["challenge"]   # geetest_challenge
result["validate"]    # geetest_validate
result["seccode"]     # geetest_seccode

Available on both CapSkip and AsyncCapSkip.

Design notes

• code keeps the raw JSON string CapSkip returns, so code ported from another solver's API still works. The parsed fields are added alongside it — unlike every other captcha type, code alone is not directly usable for GeeTest. An unparseable payload is passed through untouched rather than masked.
• Submit params are limited to the documented set — gt, challenge, pageurl, api_server, json, proxy, proxytype. All three required fields are checked locally, so a missing value fails before the round-trip instead of returning ERROR_BAD_PARAMETERS / ERROR_PAGEURL.
• Uses the longer recaptchaTimeout budget rather than defaultTimeout, since GeeTest is a real browser solve with internal retries. A caller-supplied timeout still wins. No new constructor parameter was added.
• apiServer / api_subdomain are accepted as aliases for api_server.

Also included

proxytype is now validated against the values CapSkip actually maps — HTTP, HTTPS, SOCKS5, SOCKS5H, case-insensitive — for every proxy-capable captcha type. SOCKS4 and other values previously reached the server and came back as ERROR_BAD_PARAMETERS; they now raise ValidationException locally. Image captcha is excluded so it keeps its clearer "proxy is not supported" message.

This touches reCAPTCHA and Turnstile as well as GeeTest, since they share the same submit path.

A second commit drops the "no cloud service" phrasing from the README intro; the sentence still makes the local / no-per-solve-fee point.

Testing

• 90 unit tests pass (up from 85), covering the submit payload, api_server and its aliases, proxy handling, solution-field expansion, non-JSON payloads, the required-field checks, and every accepted/rejected proxy type.
• Verified end-to-end against a live CapSkip instance: GeeTest solves and returns all three fields; image captcha, reCAPTCHA v2, and Turnstile are unaffected, and the new fields never leak into their results. Measured 10/10 GeeTest solves, averaging ~18s.

Docs

README, tutorial (new section 8), API reference, getting started, troubleshooting, and changelog all updated. Version bumped to 1.1.0; geetest added to the package keywords.

Note

The server also supports GeeTest v4 (method=geetest_v4, captcha_id), which this PR does not add.