public Builder addMethodHandler(Method method, ExtensionHandler handler) {
            methodHandlers.put(method, handler);
            return this;
        }
Adds a new extension handler for a method.

@param method The method for which an extension handler should be registered.
@param handler An {@link ExtensionHandler} instance
@return The builder instance
core/src/main/java/org/jdbi/v3/core/extension/ExtensionMetadata.java