Type Augmentation does not work in pnpm workspace monorepo

### Prerequisites

- [x] I have written a descriptive issue title
- [x] I have searched existing issues to ensure the bug has not already been reported

### Fastify version

5.6.2

### Plugin version

11.0.2

### Node.js version

24.11.1

### Operating system

macOS

### Operating system version (i.e. 20.04, 11.3, 10)

15.5

### Description

Using this plugin within a pnpm workspace monorepo does not properly augment the types on fastify's Request object.

In a standalone single package repo, it works fine, but as soon as workspaces is introduced, it fails.

Please look at the README in the linked repo to see the error.

### Link to code that reproduces the bug

https://github.com/onlywei/repro-fastify-plugins-esm-ts

### Expected Behavior

No type errors