[pm3] have tag_processor convert to toml

[shish]

$ uv run pm3-tag-processor ~/Videos/KaraKara/Cartoon/Walter\ Melon\ -\ OP.txt
category = ["cartoon"]
from = ["Walter Melon"]
use = ["opening"]
title = ["Walter Melon"]
vocalstyle = ["group"]
vocaltrack = ["on"]
length = ["short"]
lang = ["en"]
contributor = ["choco"]
date = ["1997"]
"" = ["retro"]