feat: Custom Weapon Attachments additions.

[SnivyFilms]

Description

Describe the changes
Custom Weapons now has an protected override for changing attachments
Custom Roles that are given Custom Weapon(s) on spawn, will now enforce fixed attachments if the Custom Weapon has defined attachments

What is the current behavior? (You can also link to an open issue here)
Custom Weapons currently needs to subscribe to a new ChangingAttachmentsEventArgs
Custom Roles that spawn with Custom Weapon(s) used the user's saved attachments instead of the Custom Weapon's defined attachments if the Custom Weapon has defined attachments

What is the new behavior? (if this is a feature change)
Custom Weapons now has an protected override for changing attachments
Custom Roles that are given Custom Weapon(s) on spawn, will now enforce fixed attachments if the Custom Weapon has defined attachments

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Other information:
This was built and tested on Linux only.
This is a repost of #505 but targetting LabAPI branch instead of dev

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)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing