Add formatting and linting via pre-commit hooks

[zStupan]

• Removed support for python 3.8, now only supporting >=3.9, <3.13
• Updated dependencies.
• Added pre-commit hooks for formatting and linting using the black formatter and the ruff linter. Using the default config for now.
• Fixed an error in the hill_slopes function caused by the matplotlib update.
• Updated the documentation
• Reformatted the code.
• Closes #98

We can also add https://pre-commit.ci/ to the project, so that formatting and linting can be run in pull requests.