feat: Add send_request_enqueue_strategy option to BasicCrawler

[vdusek]

Summary

Adds an opt-in send_request_enqueue_strategy: EnqueueStrategy = 'all' option to BasicCrawler so handlers can reject cross-host send_request calls. Default 'all' preserves current behavior.

Follow-up to #1864, which applied the same EnqueueStrategy mechanism to SitemapRequestLoader.

What changed

• New send_request_enqueue_strategy option on BasicCrawler / _BasicCrawlerOptions.
• When set to anything other than 'all', _prepare_send_request_function validates the target URL against the current request's loaded_url (falling back to url) via _check_enqueue_strategy and raises ValueError on mismatch.
• The closure captures the Request, so post-redirect loaded_url is the origin once set.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.48%. Comparing base (ac66b2a) to head (c5ebceb).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1865      +/-   ##
==========================================
+ Coverage   92.44%   92.48%   +0.04%     
==========================================
  Files         158      158              
  Lines       11026    11033       +7     
==========================================
+ Hits        10193    10204      +11     
+ Misses        833      829       -4     

Flag	Coverage Δ
unit	92.48% <100.00%> (+0.04%)	⬆️

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[Mantisus]

LGTM

[B4nan]

Isn't this weird? If the URL is explicitly provided, we should just follow it. If the URL was added to the queue, it must have already respected the enqueue links strategy, or again, be explicitly provided.