fix: read catppuccin-definitions.el in temp buffer instead of visiting

[ktbjob]

The catppuccin-definitions.el file is currently loaded using the find-file-noselect function, which is inappropriate for the following reasons:

• It creates a file-visiting buffer that distracts the user and clutters their post-init Emacs state.
• It runs additional code to initialize buffer major mode and so on, which are unnecessary.

This PR fixes the code to use a temporary buffer to read the contents of catppuccin-definitions.el and pass the contents to the lisp reader, avoiding the aforementioned issues.

[jtbx]

Hey thanks for taking the time to contribute! I fixed the indentation errors on your branch which caused the CI to fail.

Other than that everything looks good <3