Fix Validator protocol init to match runtime

The runtime init signature of a validator can be seen with `inspect`:

```pycon
>>> import inspect, jsonschema
>>> inspect.signature(jsonschema.validators.Draft7Validator.__init__)
<Signature (self, schema: 'referencing.jsonschema.Schema', resolver=None, format_checker: '_format.FormatChecker | None' = None, *, registry: 'referencing.jsonschema.SchemaRegistry' = <Registry (20 resources)>, _resolver=None) -> None>
```

This aligns the protocol's declared signature with that behavior more
exactly with the following changes:

`registry` is now keyword-only, not keyword-or-positional, and has a
default.

`resolver` is added to the declared signature, so users who are using
it won't see typing-time discrepancies with the runtime. It is marked
as `Any` and commented inline as deprecated, since it's unclear what
else we could do to indicate its status.
This means that code passing a resolver will continue to type check
(previously it would not).

`resolver` is the second keyword-or-positional and `format_checker` is
the third, meaning that a positional-only caller who passes, for
example: `Draft202012Validator(foo, None, bar)` will have `foo`
slotted as the schema and `bar` as the `format_checker`
This would primarily impact callers with positional-args calling
conventions, but is more reflective of what they'll see at runtime.

In order to remove `resolver` from the protocol signature, but match
the runtime signatures well, some kind of placeholder is needed to
indicate `format_checker` as positional-or-keyword. Or else, a large
number of overloads for `__init__` could be declared to try to
simulate its removal.

Author: sirosen

jsonschema/protocols.py

@@ -108,10 +108,11 @@ class Validator(Protocol):
     def __init__(
         self,
         schema: Mapping | bool,
-        registry: referencing.jsonschema.SchemaRegistry,
+        resolver: Any = None,  # deprecated
         format_checker: jsonschema.FormatChecker | None = None,
-    ) -> None:
-        ...
+        *,
+        registry: referencing.jsonschema.SchemaRegistry = ...,
+    ) -> None: ...
 
     @classmethod
     def check_schema(cls, schema: Mapping | bool) -> None: