jsonschema: options for inference (#185)

- Add ForOptions to hold options for schema inference.

- Replace ForLax with ForOptions.IgnoreBadTypes.

- Add an option to provide schemas for arbitrary types.

- Provide a default mapping from types to schemas that includes stdlib
types with MarshalJSON methods.

- Add Schema.CloneSchemas. This is needed to make copies of the schemas
in the above map: a schema cannot appear twice in a parent schema,
because schema addresses matter when resolving internal references.

mcp/tool.go

@@ -89,7 +89,7 @@ func newServerTool[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*serverTool
 func setSchema[T any](sfield **jsonschema.Schema, rfield **jsonschema.Resolved) error {
 	var err error
 	if *sfield == nil {
-		*sfield, err = jsonschema.For[T]()
+		*sfield, err = jsonschema.For[T](nil)
 	}
 	if err != nil {
 		return err