Fix Javadoc parsing issues for Checkstyle

[gianmarcoschifone]

Summary

This PR fixes Javadoc issues exposed by the updated Checkstyle Javadoc parser, specifically in relation to UnusedImportsCheck.

Details

After updating Checkstyle, several Javadocs started failing parsing and caused false positives in UnusedImportsCheck.
The root cause is stricter Javadoc parsing introduced in Checkstyle (see checkstyle/checkstyle#18059), where malformed HTML and invalid {@link} usages prevent the parser from correctly identifying type references.

The fixes in this PR:

• Correct malformed HTML in Javadocs (for example invalid <ul>/<li> structures and unclosed tags).
• Fix invalid {@link} syntax
• Ensure referenced types are properly resolvable by the Javadoc parser so that imports are correctly detected as used.

There are no behavioral or API changes. All modifications are limited to Javadoc formatting and correctness.