Fix m3u file creation, with correct metadata generation

[Silverarmor]

Title

Fix m3u file creation, with correct metadata generation

Description

Related Issue

#2251
#2246

Motivation and Context

How Has This Been Tested?

Update m3u_test file.
Ran pylint, black and mypy and edited as required.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[kalalannn]

Hello, have a specific case here. I am using spotdl with termux on android. Will this case work?

~/.../Music/Test $ pwd
/data/data/com.termux/files/home/storage/shared/MP3/Music/Test

~/.../Music/Test $ spotdl --bitrate 320k --threads 4 --m3u test.m3u 'https://open.spotify.com/playlist/...'
Processing query: https://open.spotify.com/playlist/...
Found 3 songs in Test playlist (Playlist)
Skipping Artist - Song1 (file already exists) (duplicate)
Skipping Artist - Song2 (file already exists) (duplicate)
Skipping Artist- Song3 (file already exists) (duplicate)

# Created .m3u output
~/.../Music/Test $ cat test.m3u
#EXTINF:177, Artist - Song1.mp3
#EXTINF:159, Artist - Song2.mp3
#EXTINF:142, Artist - Song3.mp3

# Wanted .m3u output
~/.../Music/Test $ cat wanted.m3u
#EXTM3U
#EXTINF:177, Artist - Song1.mp3
MP3/Music/Test/Artist - Song1.mp3
#EXTINF:159, Artist - Song2.mp3
MP3/Music/Test/Artist - Song2.mp3
#EXTINF:142, Artist - Song3.mp3
MP3/Music/Test/Artist - Song3.mp3