Fix onClientVehicleDamage not firing for boat collisions

[Flashmyname]

Summary

CBoat does not override CVehicle::VehicleDamage, its vtable slot points at the empty stub, so the hooks that raise onClientVehicleDamage for cars, bikes and planes never ran for boats. Boat collision damage is applied inline in CBoat::ProcessControl instead. This PR hooks that health subtraction the same way the existing VehicleDamage2 hooks do, with the collided vehicle as the attacker and no weapon. Damage proof boats are skipped first, as they are for cars.

Motivation

Fixes #2212. Scripts received onClientVehicleCollision and could watch a boat lose health, but never got the damage event, so the damage could not be cancelled:

addEventHandler("onClientVehicleDamage", root, function()
    cancelEvent()
end)

Weapon damage on a boat already fired the event because it goes through CVehicle::InflictDamage, which is the "not always" in the report.

Note for scripts: a boat collision now raises several damage events, one per damage tick the game applies, and cancelEvent() in the handler blocks the damage.

Test plan

Tested in game with a client resource logging the collision, the damage events and the vehicle health:

1. Ram a Speeder into a moored boat at speed.
2. The damage events fire with the loss the game applies and add up to the health drop, with the boat that was hit as the attacker.
3. With cancelEvent() in the handler the boat stays at full health.
4. Shooting a boat still fires the event as before.

Checklist

• Your code should follow the coding guidelines.
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