Update python mode marks

[galaunay]

Updates and improvements on the python.el marks.

• Remove python-mark-block as it fails to expand the selection from nested functions.
• Add er/mark-python-inside-block and er/mark-python-outside-block to expand to blocks by indentation level.
• Add er/mark-python-numbers to expand to python numbers (such as 10_000, 34.567 or 123e-35).
• Add er/mark-python-defun-or-class to expand to nested functions/classes.
• Update er/mark-outside-python-string and er/mark-inside-python-string to expand to multi-quoted string (e.g. """my docstring""") and to include string specifiers (e.g. f"variable = {var}" or b"binary string").