feat(route): add handlerPath helper to get actual route handler path

[GourangaDasSamrat]

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

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Adds a new handlerPath(c) helper to hono/route that returns the path of the actual route handler, unaffected by middleware registration order.

Problem: routePath(c, -1) breaks when middleware is registered after a route handler. Because Hono matches all routes up-front, the last entry in matchedRoutes becomes the trailing middleware (/*), not the actual handler.

app.use(async (c, next) => {
  console.log(routePath(c, -1)) // '/*' ← wrong
  await next()
})
app.get('/health', (c) => c.json({ status: 'ok' }))
app.use(async (c, next) => { await next() }) // causes the issue

Fix: handlerPath(c) finds the first matched route whose method is not ALL (i.e. not registered via app.use()), giving the correct handler path every time.

app.use(async (c, next) => {
  console.log(handlerPath(c)) // '/health' ✓
  await next()
})
app.get('/health', (c) => c.json({ status: 'ok' }))
app.use(async (c, next) => { await next() })

No breaking changes — all existing helpers are unchanged.

Closes #4609