Fix tow truck and tractor hooks on custom vehicle models

[TheCrazy17]

Summary

Extends engineRequestModel custom vehicle model support to the tow truck and tractor, so a cloned one behaves exactly like the stock model: the hook swings, it attaches to a trailer, and it bounces with movement instead of sitting rigid.

As an extra, based on a fix from SilentPatch, the tug can now hook up to trailers it couldn't before (including the utility trailer) and the artict3 can now tow a second trailer behind it, both on the stock models and on their clones.

So now, you can have B-Trains:

Motivation

Continues the ongoing series of fixes for vehicles with hardcoded native behaviour that engineRequestModel clones don't inherit (#5161, #5162, #5165, #5166, #5171, #5181). The tractor is included here since it shares the same code as the tow truck; the tug and artict3 fixes came up while working through that same area.

Part of #1861.

Test plan

Tested in game with clones of the tow truck, tractor and tug, and with both the stock and cloned artict3. Stock vehicles behave exactly as before, since the tow truck/tractor hooks are gated on the same model checks the game already used, and the tug/artict3 fixes only touch behaviour that was already broken without any custom models involved.

towtruck.zip

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.

[TheCrazy17]

@Fernando-A-Rocha 🌚

[Fernando-A-Rocha]

Christmas came early 🤩🤩🤩

[Fernando-A-Rocha]

We need to do multiplayer (2+) sync tests of vehicle towing

[TheCrazy17]

We need to do multiplayer (2+) sync tests of vehicle towing

The synchronization hasn’t been touched for now. Maybe I or someone else can improve it later, but for now it remains unchanged