fix(html2text): thread escape_backslash into escape_md_section() call

[chuenchen309]

Summary

escape_backslash is never forwarded into escape_md_section() at its call site in HTML2Text.handle_data() (crawl4ai/html2text/__init__.py), unlike its sibling flags escape_dot/escape_plus/escape_dash, which are all threaded through correctly. Because escape_md_section() has its own hardcoded default of escape_backslash=True, that default always wins — backslashes get escaped/doubled in the generated markdown regardless of what the instance (or CustomHTML2Text's own escape_backslash=False default, which is what the default markdown-generation pipeline actually uses) configures.

Fixes: n/a (no existing issue filed for this)

List of files changed and why

• crawl4ai/html2text/__init__.py — pass escape_backslash=self.escape_backslash into the escape_md_section() call in handle_data(), the same way escape_dot/escape_plus/escape_dash are already passed.
• tests/unit/test_html2text_escape_backslash.py — new unit test covering both escape_backslash=False (must not double backslashes) and escape_backslash=True (must still escape), using CustomHTML2Text directly.

How Has This Been Tested?

• Added a failing test first (TDD): with escape_backslash=False explicitly set, converting <p>Use \* for multiplication</p> produced Use \\* for multiplication (doubled) instead of the expected Use \* for multiplication — confirmed red against current code.
• After the fix, the same test goes green, and a companion test confirms escape_backslash=True still escapes as before (no default-behavior flip).
• Ran the full non-browser test subset (tests/unit/, tests/deep_crawling/, tests/regression/test_reg_extraction.py -m "not network", tests/test_source_sibling_selector.py, tests/general/test_strip_markdown_fences.py, tests/general/test_async_markdown_generator.py): same pass/fail counts before and after the change (verified via git stash/git stash pop A-B comparison) — the only failures present are pre-existing environment failures unrelated to this diff (missing local Playwright browser binary, BrowserType.launch: Executable doesn't exist), not caused by this change.
• python -m py_compile on both 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

AI disclosure

This fix was found, implemented, and verified with Claude (Anthropic) assistance in a human-in-the-loop workflow: I reviewed the exact code path, wrote/ran the failing test myself before the fix, confirmed the fix goes green, and ran the broader test subset before submitting. Commit includes a Co-Authored-By: Claude Opus 4.8 trailer for transparency.