fix(deep-crawling): allow single-label hostnames in can_process_url validation

[Bruce-Yii]

Summary

Fixes #2079

BFSDeepCrawlStrategy.can_process_url() and BestFirstCrawlingStrategy.can_process_url() rejected any URL whose netloc contains no dot (Invalid domain), silently dropping valid internal targets such as intranet hosts, localhost (with or without a port) and Docker service names during deep crawls. The error was raised before the configured FilterChain was ever applied.

The scheme (http/https) and non-empty netloc checks are kept; only the dot heuristic is removed, so https://name/xyz now passes validation and reaches the filter chain.

List of files changed and why

• crawl4ai/deep_crawling/bfs_strategy.py - Remove the dot requirement from URL validation in can_process_url.
• crawl4ai/deep_crawling/bff_strategy.py - Same fix for the best-first strategy.
• tests/deep_crawling/test_can_process_url.py - New parametrized tests covering single-label hosts, localhost with port, IP literals, rejection of missing scheme/netloc and non-http(s) schemes, and filter-chain behavior at depth > 0.

How Has This Been Tested?

• pytest tests/deep_crawling/test_can_process_url.py -v → 18 passed
• pytest tests/deep_crawling/ → 85 passed; the 2 failures in test_deep_crawl_resume_integration.py are pre-existing environment issues (they require launching a real Playwright Chromium, which is not available in this dev venv) and fail identically on unmodified develop
• ruff check --select E9,F63,F7,F82 on the changed files → clean
• python -m py_compile on the changed files → clean

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added/updated unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes