[Fix] Fix lua_shape registry to recursively resolve nested schemas

[Fix] Fix lua_shape registry to recursively resolve nested schemas

The registry's resolve_schema function was not recursively resolving
field schemas and opts.extra in table nodes, causing mixins in nested
one_of variants to never be expanded. This broke external_relay plugin
validation where rule variants with mixins were reported as having
unknown fields.

Now recursively resolves all nested schemas including field schemas,
opts.extra, and ensures mixins are properly expanded throughout the
entire schema tree.