Introduce Pipenv

Replace requirements.txt with pipenv for consistent development environments. Pipenv maintains a superior Lockfile similar to NPM. Added additional development dependencies and mypy configuration.

This contains a package update too:

• alembic from 1.12.1 to 1.13.2
• flask from 3.0.0 to 3.0.3
• SQLAlchemy from 2.0.23 to 2.0.31

pyproject.toml

+[tool.mypy]
+disallow_untyped_calls = true
+disallow_untyped_defs = true
+disallow_incomplete_defs = true
+check_untyped_defs = true
+disallow_untyped_decorators = true
+