Add ALTCHA support (v1.2.0)

[capskip]

Adds ALTCHA to the Python SDK, following the same shape GeeTest v3 used.

ALTCHA is proof-of-work rather than recognition: the site issues a challenge and the client brute-forces a number that satisfies it. There is no image, audio or text to read, so a solve is deterministic and takes milliseconds.

API

# CapSkip fetches the challenge for you
result = solver.altcha(
    url="https://example.com/signup",
    challenge_url="https://example.com/captcha/api/altcha/challenge",
)

# ...or hand it the document you already have. No network request at all.
result = solver.altcha(url="...", challenge_json={"algorithm": "SHA-256", ...})

result["token"]    # the base64 payload for the site's `altcha` form field
result["number"]   # the counter that solved it
result["code"]     # the same string as token

Available on both CapSkip and AsyncCapSkip.

Decisions worth reviewing

• challenge_json accepts a dict, serialized for you — a form body cannot carry Python's repr. A dict that reached the wire unserialized would draw ERROR_BAD_PARAMETERS.
• Both challenge params may be sent; the inline document wins. That matches CapSkip, which is deliberately more permissive here than 2Captcha's mutually-exclusive spelling.
• Uses defaultTimeout, not recaptchaTimeout. This is CPU work, not a browser solve — unlike GeeTest and reCAPTCHA.
• A proxy applies only to the challenge_url fetch; an inline challenge never touches the network.
• Method named altcha(), matching 2captcha-python exactly and the house style used by geetest() / turnstile().

Testing

• 121 tests pass (pytest tests/), up from 105 — new tests/test_altcha.py, tests/test_async_altcha.py, and integration tests driving real HTTP against the mock server, which now serves a genuine base64 ALTCHA payload so the decode path is actually exercised.
• Verified end-to-end against a running CapSkip on :8080, on both the inline and the challenge_url fetch paths, with a challenge whose answer was known in advance — the SDK recovered the exact counter each time.