feat: add middleware meta support and defineMiddlewareRoute utility

[productdevbook]

Closes #1153

Description

This PR introduces two new features to improve middleware handling in h3:

1. Middleware meta support: Adds metadata support to middleware, similar to how routes can have meta
2. defineMiddlewareRoute utility: A new utility function for defining middleware as plugins, following the same pattern as defineRoute

Changes

1. Middleware Meta Support

• Added meta?: H3RouteMeta to MiddlewareOptions type
• Updated normalizeMiddleware to handle meta and store it in event.context.matchedMiddleware
• Added matchedMiddleware array to H3EventContext type to track matched middleware with their metadata

2. defineMiddlewareRoute Utility

• New utility function that returns an H3Plugin for middleware registration
• Supports path patterns, HTTP method filtering, and metadata
• Uses the existing defineMiddleware function internally
• Consistent API with defineRoute

Usage Examples

// Define middleware with meta
const authMiddleware = defineMiddlewareRoute({
  path: '/api/**',
  methods: ['POST', 'PUT', 'DELETE'],
  meta: { 
    requiresAuth: true,
    rateLimit: { interval: '1m', tokensPerInterval: 10 }
  },
  handler: async (event, next) => {
    if (\!event.context.user) {
      return new Response('Unauthorized', { status: 401 });
    }
    return next();
  }
});

// Register the middleware
app.register(authMiddleware);

// Access meta in handlers
app.get('/api/users', (event) => {
  // Access route meta
  const routeMeta = event.context.matchedRoute?.meta;
  
  // Access middleware meta
  const middlewareMeta = event.context.matchedMiddleware;
  // [{ route: '/api/**', meta: { requiresAuth: true, ... } }]
  
  return { users: [] };
});

Benefits

• Consistent API between routes and middleware
• Ability to attach configuration to middleware
• Plugin-based middleware definition for better modularity
• Follows existing h3 patterns and conventions

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View logs

[pi0]

app.use already adds matching support using normalizeMiddleware internal (see here > here so we don't need to do it again here.

Also #1153 (comment), we could add this functionality to existing defineRoute utility.

[pi0]

Please remove it from this PR. We need runtime implementation and one PR per feature!