feat(docloaders): add Xquik tweet loader

[kriptoburak]

Problem

Public X status pages can return login or client-rendered shells to the generic Chromium loader. SmartScraperGraph then lacks stable post data for extraction.

Changes

• Add XquikLoader for public x.com and twitter.com status URLs or numeric tweet IDs.
• Retrieve the published tweet response through the optional x_twitter_scraper SDK.
• Pass structured JSON and source metadata into the existing graph pipeline.
• Skip HTML-to-Markdown conversion for the structured Xquik response.
• Document installation, configuration, and a complete SmartScraperGraph example.
• Cover URL validation, request order, client ownership, graph routing, metadata, and FetchNode behavior.

The SDK stays optional. Users install it with scrapegraphai when they enable the xquik configuration.

Tests

• 107 deterministic unit tests passed, including the repository CI suite and 12 Xquik tests.
• Black, isort, and Ruff passed for every changed Python file.
• Mypy passed for the new loader and its unit tests.

Security

The examples contain placeholder environment variables only. The integration uses the published Xquik SDK contract and public tweet data.