refactor: enforce stricter type hints (#91)

LSP was screaming at me so I decided to just address it to get it off my
screen.

+ Fixed the type hints
:= Modified and added type hints for certain functions and variables in
most of the files in the utils/ folder (and some in the subcommands/
folder) for clarity and so pyright's type checker wouldn't cry.
:+ To resolve certain type issues, I had to add a bit more tiny
additional code such as, additional checks if a variable is None, a tiny
class in utils/material/generator.py to resolve the constructor usage
mismatch between what the DynamicScheme accepts and what the code
actually passes, and etc.
- Renamed certain functions and variables for clarity and also for some
to not collide with pre-existing definitions from well-known library
imports.
+ PIL has reorganized their code a bit, so the code is made to reflect
their new definitions.
= Reorganized the single import statement for "colourfulness" in
utils/wallpaper.py to be close to the top.
(I think that's it)

Side Effects?:
Everything should work the same as no logic change was done whatsover
(unless we consider the added if statements for type checking as a logic
change). I've tested it, everything seems to be in urdir.

src/caelestia/utils/notify.py

@@ -1,7 +1,7 @@
 import subprocess
 
 
-def notify(*args: list[str]) -> str:
+def notify(*args: str) -> str:
     return subprocess.check_output(["notify-send", "-a", "caelestia-cli", *args], text=True).strip()