patch: work around pip's secure-install bug; bump version

- upstream issue: https://github.com/pypa/pip/issues/9644
- runs tests within a container, uses the same `dockerfile`
- ignores `pdm.lock`, removes `requirement.txt`
- update manual contribution steps
- bumps project version

**Related Items**

_Issues_

- Closes #137

.gitignore

@@ -85,23 +85,27 @@ ipython_config.py
 # pyenv
 #   For a library or package, you might want to ignore these files since the code is
 #   intended to run in multiple environments; otherwise, check them in:
-# .python-version
+.python-version
 
 # pipenv
 #   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
 #   However, in case of collaboration, if having platform-specific dependencies or dependencies
 #   having no cross-platform support, pipenv may install dependencies that don't work, or not
 #   install all needed dependencies.
-#Pipfile.lock
+Pipfile.lock
 
 # poetry
 #   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
 #   This is especially recommended for binary packages to ensure reproducibility, and is more
 #   commonly ignored for libraries.
 #   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
-#poetry.lock
+poetry.lock
 
 # pdm
+#   Similar to poetry.lock, it is generally recommended to include pdm.lock in version control.
+#   https://pdm.fming.dev/latest/usage/project/#working-with-version-control
+#   However, this project does not rely on pdm for production.
+pdm.lock
 .pdm-python
 
 # PEP 582; used by e.g. github.com/David-OConnor/pyflow