Display stacktrace when logging an error

### Prerequisites

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

### 🚀 Feature Proposal

When an error is logged, the back-trace could be displayed alongside the error.
Although this would obviously break with the name of this library as it would require multiple lines to do so. (I'd argue it is a worthy exception though.)

### Motivation

@fastify/one-line-logger is typically suggested for use in dev environments. In a dev environment it is very useful to be able to see the back-trace on an error, in order to debug the issue.

### Example

Vanilla pino-pretty will do this currently, albeit in not so pretty a way.

| Current @fastify/one-line-logger | Vanilla pino-pretty |
| --- | --- |
| | |

The issue names no files, tests, or entry points. Start by tracing how one-line-logger formats logged errors and compare that output with vanilla pino-pretty. Define how a backtrace should appear while preserving the logger's intended output, then verify the resulting error output against the proposal.

Written by the indexing model from the issue text.