Quarto Lua Modules 2.4.0

• feat: Add Checker:option, which returns the value the schema resolves an option to. An extension no longer decides for itself what counts as true, so enabled: no means the same thing in every extension.
• feat: Add Checker:attributes, which checks one element's attributes against the attributes section and returns what they resolve to. Both the element's own group and _any apply, the named group last.
• docs: State that Checker:options reads the metadata of its first call only. A later call returns what the first call resolved, so a caller that needs a second document checked builds a second checker.