Add GeeTest v3 support (v1.1.0)

[capskip]

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

What's new

$result = $solver->geetest(
    '81388ea1fc187e0c335c0a8907ff2625',
    '7cf6a8b1a2c34d5e6f7089abcdef0123',
    'https://example.com/login'
);

$result['challenge'];   // geetest_challenge
$result['validate'];    // geetest_validate
$result['seccode'];     // geetest_seccode

Available on CapSkip and, by inheritance, 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 option 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.

The README intro also drops its "no cloud service" phrasing; the sentence still makes the local / no-per-solve-fee point.

Testing

• 71 unit tests pass (up from 63), 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 — 15/15 checks, from source and from a composer-installed copy in a clean consumer project (which also exercises the PSR-4 + files autoload config). GeeTest solves and returns all three fields; image captcha, reCAPTCHA v2, and Turnstile are unaffected, and the new fields never leak into their results.
• composer validate --strict passes.

Docs

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

Note

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