$dynamicRef does not implement 2020-12 dynamic scope semantics (7 core TCK tests skipped)

### Version

5.2.0-SNAPSHOT (master), affects 5.x releases as well

### Context

Seven **core** (non-optional) `draft2020-12/dynamicRef` tests from the official test suite have been listed in `unsupported-tck-tests.properties` since 2022. Unlike the rest of that file (format-as-annotation, ECMA regex, idn-hostname — genuinely optional features), these mask real `$dynamicRef` conformance bugs in `SchemaValidatorImpl`:

1. **Dynamic scope is never left.** `$dynamicAnchor`s pushed into `dynamicContext` are only popped at the end of a full `validate` pass — the `$ref`/draft-4/7 early-return paths skip the pop, so anchors from sibling scopes stay resolvable ("after leaving a dynamic scope, it should not be used by a $dynamicRef").
2. **No fallback to `$ref` semantics.** A `$dynamicRef` whose target anchor is a plain `$anchor`, or with no matching `$dynamicAnchor` yet encountered, is silently ignored instead of behaving like a normal `$ref` ("A $dynamicRef to an $anchor in the same schema resource should behave like a normal $ref to an $anchor").
3. **Resolution is encounter-based, not resource-based.** The spec resolves to the first schema *resource* in the dynamic scope defining a matching `$dynamicAnchor`, whether or not evaluation visited the anchored subschema; the implementation only considers anchors whose subschema was visited ("The recursive part is not valid against the root", "first_scope is not in dynamic scope").

### Steps to reproduce

Remove the `draft2020-12/dynamicRef` entries from `src/test/resources/unsupported-tck-tests.properties` and run `TCKTest`: 7 failures.

### Do you have a reproducer?

Yes — the official test suite itself; PR incoming that fixes the implementation and un-skips the tests.

Start with SchemaValidatorImpl and the seven draft2020-12/dynamicRef cases listed in src/test/resources/unsupported-tck-tests.properties. Remove those entries locally and run TCKTest to observe the failures, then trace dynamicContext handling, $dynamicRef fallback, and resource-based resolution. Done means the seven core tests pass without masking the failures.

Written by the indexing model from the issue text.