feat(vehreg): Add Make and Year support, fix customData nil bug

[FearlessNite345]

Improve vehreg Custom Vehicle Support

This update improves the customData system in the vehreg submodule by making fields more flexible and fixing a critical bug that prevented the data from being used properly.

Changes:

• Made make and year optional in the customData config entries.
• Fixed a bug where customData was accessed using customData[spawncode], but the config was structured as an array, not a key-value table. Now it correctly iterates and matches entries by spawncode.

Benefits:

• Fixes an issue where customData was silently ignored due to improper access.
• Adds flexibility by allowing make and year to be omitted if not needed.

Example Usage:

customData = {
    ["adder"] = {
        model = "Adder",
        make = "Truffade",
        year = 2013
    },
    ["blista"] = {
        model = "Blista"
        -- make and year are optional
    }
}

[Fireant456]

Will be merged in with #69