Play unit script animation during wind up

Add the possibility of playing an animation during its pre-attack delay (“wind up”) as there is no built-in support for it. We talked about adding a CEG tag to the weapon during pre-attack (as a warm-up alert), but having an animation event/callback in the script environment would also be very important.

Reference: Note the nuke cannon here has a setup animation, before even being able to start aiming:
https://youtu.be/o-3IsmwvU8o?t=20

Related to: https://github.com/beyond-all-reason/spring/pull/1581

Start by reviewing related pull request 1581 and the engine's weapon pre-attack or wind-up handling. Define how a script-visible animation event or callback should work during the delay, and consider the proposed CEG warm-up tag; done when the chosen mechanism supports the requested pre-attack animation behavior.

Written by the indexing model from the issue text.