fix: skip regex checks on autolink URLs

[Kubudak90]

Fixes #91.

Autolinks like \u003chttps://example.com/eip7002\u003e were incorrectly checked against regex patterns, causing false positives when URLs contained prohibited patterns.

Root Cause

The visitor traverses all text nodes, including autolink URL text, which shouldn't be checked against regex patterns.

Solution

Use a link URL stack to track when we're inside a link:

1. pushes the link URL onto the stack
2. checks if text matches the top URL — if so, it's an autolink and we skip the pattern check
3. pops the URL from the stack

This correctly handles:

• Autolinks: \u003curl\u003e — URL text is not checked
• Regular links: text — link text is still properly checked
• Nested links: stack handles nesting correctly

Changes

• : add stack-based autolink detection
• : regression tests

All existing tests pass.

[Kubudak90]

Closing in favor of #152 which has the same fix with a cleaner commit history.