feat: ignore .disabled files (closes #13)

[Lemmmy]

This PR adds a check for sibling .disabled in the local file validation routine. This solves #13, and will also work for resource pack files and others as mentioned in #51. There is still future room for Packwiz to do its own things as mentioned in #6 but this is a stop-gap solution to maintain support with MultiMC-based launchers.

[Lemmmy]

Apologies for the indentation mistake there - editor misconfiguration on my end.

[comp500]

This change only stops packwiz-installer from redownloading a file when it is initially disabled, so updates to disabled mods will still be downloaded and need to be disabled again. Mod disabling needs to be synced with the optional mods system, so the optional mods dialog can be used to re-enable an optional mod that was disabled in the launcher.

I haven't looked at the relevant code in a while, but I think I was going to implement this by treating all files like optional files internally (but only showing mods marked as optional by default), and when a .disabled file is scanned the relevant file is marked as disabled.