feat: provide Request instances in skipped request callbacks

[vdusek]

on_skipped_request callbacks can now receive the full Request object instead of only the URL string, so handlers can access request metadata such as user_data.

This stays backward compatible by dual-dispatching on the type annotation of the callback's first parameter: annotate it as Request to receive the object, while a str annotation (or no annotation) keeps receiving the URL string as before. Skipped URLs are normalized to Request once at the choke points (add_requests and both extract_links implementations), the duplicated request-building helper was extracted to crawlee._utils.requests.create_request_from_options, and link extraction now applies transform_request_function to robots-skipped requests for consistency with enqueued ones.

Reworked from #1927 (original author inactive).

[codecov]

Codecov Report

❌ Patch coverage is 92.77108% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.17%. Comparing base (a58687e) to head (608fbb6).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/crawlee/crawlers/_basic/_basic_crawler.py	83.33%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1999      +/-   ##
==========================================
+ Coverage   93.09%   93.17%   +0.08%     
==========================================
  Files         167      167              
  Lines       11775    11815      +40     
==========================================
+ Hits        10962    11009      +47     
+ Misses        813      806       -7     

Flag	Coverage Δ
unit	93.17% <92.77%> (+0.08%)	⬆️

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