Fix: Migración a pyproject.toml y poetry

- Reemplaza setup.py/setup.cfg por pyproject.toml (PEP 621) + poetry.lock
- Dev dependencies en [tool.poetry.group.dev.dependencies]
- Elimina requirements_dev.txt (deps dev en pyproject.toml)
- Actualiza tox.ini, Makefile, Makefile.dev, Dockerfile y docs

docs/installation.rst

@@ -44,7 +44,7 @@ Once you have a copy of the source, you can install it with:
 
 .. code-block:: console
 
-    $ python setup.py install
+    $ pip install .
 
 
 .. _Github repo: https://github.com/bit4bit/facho