feat: streamline setupMiddlewares usage

[chenjiahan]

Summary

The dev.setupMiddlewares requires the user to pass an array which is redundant.

This PR allows dev.setupMiddlewares to pass a function directly to streamline usage.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR refactors dev.setupMiddlewares to accept a single function or an array of functions, removing the need for redundant array syntax.

• Change type signature to SetupMiddlewaresFn | SetupMiddlewaresFn[]
• Update core middleware application to use castArray
• Refresh documentation and tests to use the new function-only syntax

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
website/docs/{zh,en}/guide/basic/server.mdx	Updated examples to drop the array wrapper around middleware fn
website/docs/{zh,en}/config/dev/setup-middlewares.mdx	Adjusted type definitions and examples for union syntax
packages/core/src/types/config.ts	Changed setupMiddlewares type to accept fn or fn array
packages/core/src/server/devMiddlewares.ts	Added castArray import and loop to handle single or array
e2e/cases/server/**/*	Simplified test configs to use direct function syntax

Comments suppressed due to low confidence (1)

e2e/cases/server/setup-middlewares/index.test.ts:4

• Add a test case that passes setupMiddlewares as an array (the old syntax) to verify backward compatibility with the new union type.

test('should apply custom middleware via `setupMiddlewares`', async ({