Ignore references overlapping inline code spans

[thynomex]

Fixes #269

/claim #269

This fixes the false unresolved-reference diagnostic for literal [[ and ]] markers inside inline code spans.

Root cause: the codeblock filter only ignored references fully contained inside a code span. The reported text can create a single wikilink regex match that starts inside the first inline code span and ends inside the second, so it was not fully contained by either span.

Changes:

• Add range-overlap detection for Rangeable values.
• Filter references that overlap an inline/fenced code range when references_in_codeblocks is disabled.
• Add a regression test for the reported inline-code [[ / ]] case while preserving a normal wikilink outside code.

Validation:

• cargo test references_overlapping_inline_code_are_ignored -> passed
• cargo fmt --check -> passed
• cargo test -> 75 passed

[thynomex]

/claim #269