Check for new versions

## Overview

Add a check to see if a new version of prune exists and if it does suggest a `pip install auditree-prune --upgrade`.

## Requirements

- Check for new version pre execution of a command
- If exists suggest `pip install auditree-prune --upgrade` otherwise do nothing

## Approach

See req

## Security and Privacy

N/A

## Test Plan

TBD

Locate the command execution entry point and read how prune runs commands before execution. Check the existing project and test setup, then verify that a newer version produces the requested upgrade suggestion while an up-to-date version produces no message.

Written by the indexing model from the issue text.