…ders

- crawley.http.playwright.PlaywrightRequestManager: render pages with a
  headless browser (lazy import), with per-host throttling and retries; wired
  into the engine via `render_js = True` and `playwright_options`. Optional
  extra `crawley[js]`.
- Docs: new "Spiders" page (Request/callbacks/follow, item pipelines,
  CrawlSpider/LinkExtractor, SitemapSpider, JS rendering); API reference and
  nav updated.
- examples/06_spider.py (callback spider + pipeline), indexed and test-covered.
- README "Spiders" section; CHANGELOG updated.

Tests (180 -> 187): test_playwright (render path mocked, no browser needed)
plus the spider example.

- crawley.stats.StatsCollector: per-crawl counters (requests, responses,
  status/<code>, request_errors, robots_blocked, items/items_dropped, elapsed),
  exposed as crawler/spider `stats` and logged on finish.
- crawley.http.cache.HttpCache: on-disk response cache keyed by
  method+url+body. Enable with `http_cache = True` / `http_cache_dir`; wired
  into RequestManager, FastRequestManager and the Playwright manager.
- crawley.spider.FormRequest + FormRequest.from_response(): read a <form>,
  pre-fill inputs/selects/textareas, honour its method (GET -> query string),
  override fields via formdata.

Docs (crawler stats/cache, spiders forms, API reference) and CHANGELOG updated.
Tests (187 -> 201): test_stats, test_cache, test_forms; conftest serves
/login-form.

- crawley.middlewares.DownloaderMiddleware: process_request / process_response
  / process_exception chains (sync or async) wrapping every Spider download.
  process_request may short-circuit with a Response or reschedule a Request;
  process_exception can recover from errors.
- crawley.http.autothrottle.AutoThrottle: adapt the per-host delay to the
  observed response latency (target_concurrency, start/max delay). Enable with
  `autothrottle = True`; Response now carries `.latency` (httpx elapsed /
  measured render time), fed to the per-host rate limiter.

Docs (spiders middlewares, politeness AutoThrottle, API reference) and
CHANGELOG updated. Tests (201 -> 213): test_middlewares, test_autothrottle.