Ignore wikilinks overlapping inline code

[hendkai]

Fixes #269

/claim #269

Summary

• Treat references that overlap inline/fenced code ranges as ignored when references_in_codeblocks is disabled.
• Prevents separated literal code spans like `[[` and `]]` from being joined into a false wikilink.
• Adds a regression test that preserves normal wikilinks outside code.

Verification

• cargo fmt --check
• cargo test