docs: fix up cookbook debounce typing (#7643)

Update index.mdx

## Summary
This PR addresses a TypeScript error related to the use of readonly tuple types in conjunction with QRL.

## Problem
Using a readonly tuple type A extends readonly unknown[] caused the following TypeScript diagnostic when invoking a QRL:

Argument of type '[...A]' is not assignable to parameter of type 'QrlArgs<(...args: A) => R>'. [2345]

## Root Cause
This appears to be a type compatibility issue between the readonly tuple spread ([...A]) and the expected QrlArgs type in the QRL function signature. It's possible there's an edge case or mismatch in how QrlArgs<(...args: A) => R> resolves in the presence of readonly tuples, or perhaps recent TypeScript updates introduced stricter rules around readonly spreads.

## Solution
The fix involves removing the readonly modifier from the generic tuple constraint:

- A extends readonly unknown[]
+ A extends unknown[]

This ensures compatibility with the QRL's expected argument types while preserving type safety.

### Notes
Further investigation might be warranted to confirm whether this is a TypeScript typing nuance or a limitation in the Qwik QRL typings themselves.

Author: extrordinaire

packages/docs/src/routes/docs/cookbook/debouncer/index.mdx

@@ -31,7 +31,7 @@ The Qwik framework provides unique capabilities for managing state and effects i
 
 <CodeFile src="/src/routes/demo/cookbook/mediaController/index.tsx">
 ```tsx
-export const useDebouncer = <A extends readonly unknown[], R>(
+export const useDebouncer = <A extends unknown[], R>(
   fn: QRL<(...args: A) => R>,
   delay: number,
 ): QRL<(...args: A) => void> => {
@@ -98,7 +98,7 @@ We can leverage Qwik's `implicit$FirstArg` function to create a `useDebouncer$`
 This is how Qwik actually implements all of its built-in $ hooks.
 
 ```tsx
-export const useDebouncerQrl = <A extends readonly unknown[], R>(
+export const useDebouncerQrl = <A extends unknown[], R>(
   fn: QRL<(...args: A) => R>,
   delay: number,
 ): QRL<(...args: A) => void> => {