Update validation middleware

- Move to separate directory
- Add TypedRequest utility fn
- Utilize as middleware instead of function

src/server/validations/songs.validation.ts

@@ -0,0 +1,22 @@
+import { z } from 'zod';
+import {
+  idValidation,
+  paginationValidation,
+  serverFolderIdValidation,
+} from './shared.validation';
+
+const list = {
+  body: z.object({}),
+  params: z.object(idValidation),
+  query: z.object({
+    ...paginationValidation,
+    ...serverFolderIdValidation,
+    albumIds: z.optional(z.string()),
+    artistIds: z.optional(z.string()),
+    songIds: z.optional(z.string()),
+  }),
+};
+
+export const songsValidation = {
+  list,
+};