Modernize Python code to 3.10+ idioms and add type hints

[ardiloot]

• Add type hints to all Python function signatures
• Replace % string formatting with f-strings
• Use argumentless super() (Python 3+)
• Use modern class syntax (class Foo: instead of class Foo(object):)
• Replace os.path with pathlib.Path
• Use context managers for file handles
• Replace type() == with isinstance()
• Replace pylab with matplotlib.pyplot
• Replace scipy.real/imag with np.real/np.imag
• Replace float('inf') with math.inf
• Replace np.arange with range() for loop indexing
• Use specific exception types instead of bare Exception
• Remove Eclipse/PyDev IDE comments
• Remove dead if __name__ == '__main__': pass blocks
• Add __all__ to NonlinearTMM/__init__.py
• Clean up docs/conf.py (remove encoding comment, update master_doc to root_doc)
• Add .vscode/settings.json