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/parser.py

@@ -6,7 +6,7 @@ from caelestia.utils.scheme import get_scheme_names, scheme_variants
 from caelestia.utils.wallpaper import get_wallpaper
 
 
-def parse_args() -> (argparse.ArgumentParser, argparse.Namespace):
+def parse_args() -> tuple[argparse.ArgumentParser, argparse.Namespace]:
     parser = argparse.ArgumentParser(prog="caelestia", description="Main control script for the Caelestia dotfiles")
     parser.add_argument("-v", "--version", action="store_true", help="print the current version")