Close elements emitted at the nesting limit

[jmanico]

The tag balancer emitted an element at the configured nesting limit but used one-level-stricter checks when closing it. Explicit, implicit, ancestor, and document-end closes could therefore leave sanitized HTML unbalanced.

Track whether each logical stack entry was actually sent downstream and use that fact for every close path. This also keeps close decisions correct when setNestingLimit changes while a document is open.

Regression coverage includes exact serialization, browser-tree equality, sanitizer idempotence, explicit and implicit closes, ancestor closes, document close, pushed-out/resumed table content, and a limit raise after an un-emitted resumed formatting element.

Validation:

• ./mvnw clean verify with Homebrew OpenJDK 11, 17, 21, and 25
• all fuzzer tests with -Djunit.seed=485, 342, and 20260911
• 20,000 deterministic known-tag streams with legal mid-document limit changes and downstream event-balance checks

Closes #485