fix(node): loosen type of LoadFnOutput

A `LoadHook` accepts a `LoadHookContext` object having a `format` of `string | null | undefined`.

`LookHook` implementors often want to pass this value through ([example from docs](https://nodejs.org/api/module.html\#asynchronous-version), which suggests to me that a) it can be falsy, and b) it should be a looser type as established for `ResolveFnOutput` in DefinitelyTyped#71493).

A consequence of this is that `ModuleFormat` is no longer referenced anywhere; it can be removed.

Author: boneskull

types/node/module.d.ts

@@ -334,14 +334,6 @@ declare module "module" {
         interface ImportAttributes extends NodeJS.Dict<string> {
             type?: string | undefined;
         }
-        type ModuleFormat =
-            | "builtin"
-            | "commonjs"
-            | "commonjs-typescript"
-            | "json"
-            | "module"
-            | "module-typescript"
-            | "wasm";
         type ModuleSource = string | ArrayBuffer | NodeJS.TypedArray;
         /**
          * The `initialize` hook provides a way to define a custom function that runs in
@@ -419,7 +411,7 @@ declare module "module" {
             importAttributes: ImportAttributes;
         }
         interface LoadFnOutput {
-            format: ModuleFormat;
+            format: string | null | undefined;
             /**
              * A signal that this hook intends to terminate the chain of `resolve` hooks.
              * @default false

types/node/test/module.ts

@@ -204,6 +204,14 @@ Module.Module === Module;
             };
         }
 
+        if (format === null) {
+            return {
+                format,
+                shortCircuit: true,
+                source: "...",
+            };
+        }
+
         return nextLoad(url);
     };
 }