🐛 Fix code span padding around non-space whitespace

[hulkbig]

Summary

Use strip(" ") when checking whether a code span consists entirely of spaces. Python's argumentless strip() also removes tabs and other Unicode whitespace, which incorrectly prevents removal of the surrounding U+0020 padding.

This follows CommonMark 0.31.2 §6.1: normalize line endings, then remove one space from each end unless the content consists entirely of spaces.

Reproduction

from markdown_it import MarkdownIt

MarkdownIt("commonmark").renderInline("` \t `")
# Before: "<code> \t </code>"
# After:  "<code>\t</code>"

Related #438, specifically its code span padding example. This change is limited to padding normalization; the backtick lookahead behavior discussed in #439 is unchanged.

Tests

• Add 52 parameterized cases covering tabs, NBSP and other whitespace, all-space content, one-sided padding, multiple spaces, line-ending normalization, and one- or two-backtick delimiters. Check rendered HTML and parsed code-token content.
• Before the fix: 28 new cases fail and 24 pass. After the fix: all 52 pass.
• tox -e py310,py311,py312,py313: 1,084 tests pass on each CPython version.
• pre-commit run --all-files: passes, including Ruff, formatting, and mypy.

AI assistance

AI assistance was used for diagnosis, implementation, regression tests, validation, and PR preparation. A separate AI agent independently reviewed the change.