fix: correct Zod plugin handler selection

Fix switch statement ordering in Zod plugin to properly route
compatibilityVersion values to the correct handlers:
- case 3: uses handlerV3
- case 4: uses handlerV4
- default: uses handlerV4

Previously case 4 was before case 3, causing all versions
to fallthrough to handlerV4.

Updated snapshots for both Zod v3 and v4 tests to reflect
the corrected plugin behavior.

Author: Mxwllas

packages/openapi-ts-tests/zod/v3/__snapshots__/2.0.x/mini/default/zod.gen.ts

@@ -1,21 +1,21 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import * as z from 'zod/v4-mini';
+import { z } from 'zod';
 
 export const zFoo = z.object({
-    bar: z.optional(z.int()),
-    foo: z._default(z.coerce.bigint(), BigInt(0)),
+    bar: z.number().int().optional(),
+    foo: z.coerce.bigint().default(BigInt(0)),
     id: z.string()
 });
 
 export const zBar = z.object({
-    foo: z.int()
+    foo: z.number().int()
 });
 
 export const zPostFooData = z.object({
-    body: z.optional(z.never()),
-    path: z.optional(z.never()),
-    query: z.optional(z.never())
+    body: z.never().optional(),
+    path: z.never().optional(),
+    query: z.never().optional()
 });
 
 /**