Dependency on python package 'future' seems to be missing (problem after installing with pipx)

Tested with:
- mavproxy 1.8.74
- Ubuntu 24.04
- pipx

Since a normal `pip install ...` doesn't work under Ubuntu 24 as easily as e.g. under Ubuntu 22 (without virtual environments), I couldn't follow the instructions [here](https://ardupilot.org/mavproxy/docs/getting_started/download_and_installation.html#linux) and it seemed reasonable to use pipx instaed. With pipx, I had to manually install the package `future` (using `pipx runpip mavproxy install future`) for mavproxy to work.

Here the terminal output for details:
```bash
$ pipx install mavproxy
installed package mavproxy 1.8.74, installed using Python 3.12.3
These apps are now globally available
- MAVExplorer.py
- mavflightview.py
- mavpicviewer.py
- mavproxy.py
- mp_slipmap.py
- mp_tile.py
done! ✨ 🌟 ✨
$ mavproxy.py
Traceback (most recent call last):
File "/home/michael/.local/bin/mavproxy.py", line 39, in
from MAVProxy.modules.lib import rline
File "/home/michael/.local/share/pipx/venvs/mavproxy/lib/python3.12/site-packages/MAVProxy/modules/lib/rline.py", line 8, in
from future.builtins import input
ModuleNotFoundError: No module named 'future'
$ pipx runpip mavproxy list
Package Version
--------- -------
fastcrc 0.3.6
lxml 6.1.1
MAVProxy 1.8.74
numpy 2.5.0
pip 26.1.2
pymavlink 2.4.49
pynmeagps 1.1.5
pyserial 3.5
$ pipx runpip mavproxy install future
Collecting future
Using cached future-1.0.0-py3-none-any.whl.metadata (4.0 kB)
Using cached future-1.0.0-py3-none-any.whl (491 kB)
Installing collected packages: future
Successfully installed future-1.0.0
$ mavproxy.py
WARNING: You should uninstall ModemManager as it conflicts with APM and Pixhawk
Auto-detected serial ports are:
/dev/ttyS0
/dev/ttyS1
```

Start with the MAVProxy package dependency metadata and the import in MAVProxy/modules/lib/rline.py, reached from the mavproxy.py entry point. Ensure a fresh pipx installation includes the future package, then run mavproxy.py and confirm it starts without the ModuleNotFoundError.

Written by the indexing model from the issue text.