[jay23606]

Closes #43.

The problem

Many functions and methods in adafruit_framebuf.py have no type annotations, so mypy reports them as missing annotations.

The change

• Wrap from typing import Any, Optional, Tuple, Union in try/except ImportError, because typing does not exist on CircuitPython.
• Add parameter and return annotations to all 43 functions and methods in the module. The forward reference to FrameBuffer is a string, and annotations are not evaluated on CircuitPython.
• No runtime behaviour changes; only def lines and the import block are touched.

Testing

Added tests/test_annotations.py, which uses inspect to check that every function and method in the module has a return annotation and annotated parameters. After the change, it passes:

python -m unittest discover -s tests -p "test_annotations.py"

Regression test: tests/test_annotations.py checks the annotations added by this change.

Fixes #43