feat: pluggable paymentHandler hook for x402 integration

[acedatacloud-dev]

What

Adds a pluggable paymentHandler (TS) / payment_handler (Python) hook to the SDK transport. When the API returns 402 Payment Required, the transport now:

1. parses the response body
2. passes the accepts list to the configured handler
3. retries the request once with the headers the handler returns (typically X-Payment)

Why

Previously the SDK only supported Bearer-token auth, and @acedatacloud/x402-client had to reinvent its own HTTP client to do x402 flows. That meant two parallel ways of calling the same APIs, and features like task polling / streaming / retries were missing from the x402 path.

With this hook, the SDK stays the single entry point for every AceDataCloud endpoint, and X402Client becomes a small adapter that produces a paymentHandler.

Usage

import { AceDataCloud } from '@acedatacloud/sdk';
import { createX402PaymentHandler } from '@acedatacloud/x402-client';

const client = new AceDataCloud({
  paymentHandler: createX402PaymentHandler({
    network: 'base',
    evmProvider: window.ethereum,
    evmAddress: '0x...',
  }),
});

await client.openai.chat.completions.create({ ... });

Python accepts any callable returning {"headers": {"X-Payment": ...}} (sync or async).

Changes

• TS: new runtime/payment.ts, Transport accepts paymentHandler, apiToken becomes optional when a handler is supplied
• Python: new _runtime/payment.py, SyncTransport / AsyncTransport accept payment_handler, async transport awaits coroutines transparently
• READMEs (root, TS, Python) updated with the x402 integration pattern
• All existing tests still pass (22 passed, 29 skipped)

Companion PR in X402Client: https://github.com/AceDataCloud/X402Client/pulls (will be opened next).