Migrate all mechs to PartAssembly and remove legacy MechAssemblySystem (#39027)

* Removed the old MechAssembly system and component.
Converted all mechs to use the unified PartAssembly system.
Removed dismantling mechs during assembly logic to simplify the code.

* Delete Chassis via migration

Content.Server/Mech/Systems/MechAssemblySystem.cs

@@ -1,67 +0,0 @@
-using Content.Server.Mech.Components;
-using Content.Shared.Interaction;
-using Content.Shared.Tag;
-using Content.Shared.Tools.Components;
-using Content.Shared.Tools.Systems;
-using Robust.Server.Containers;
-using Robust.Shared.Containers;
-
-namespace Content.Server.Mech.Systems;
-
-/// <summary>
-/// Handles <see cref="MechAssemblyComponent"/> and the insertion
-/// and removal of parts from the assembly.
-/// </summary>
-public sealed class MechAssemblySystem : EntitySystem
-{
-    [Dependency] private readonly ContainerSystem _container = default!;
-    [Dependency] private readonly TagSystem _tag = default!;
-    [Dependency] private readonly SharedToolSystem _toolSystem = default!;
-
-    /// <inheritdoc/>
-    public override void Initialize()
-    {
-        SubscribeLocalEvent<MechAssemblyComponent, ComponentInit>(OnInit);
-        SubscribeLocalEvent<MechAssemblyComponent, InteractUsingEvent>(OnInteractUsing);
-    }
-
-    private void OnInit(EntityUid uid, MechAssemblyComponent component, ComponentInit args)
-    {
-        component.PartsContainer = _container.EnsureContainer<Container>(uid, "mech-assembly-container");
-    }
-
-    private void OnInteractUsing(EntityUid uid, MechAssemblyComponent component, InteractUsingEvent args)
-    {
-        if (_toolSystem.HasQuality(args.Used, component.QualityNeeded))
-        {
-            foreach (var tag in component.RequiredParts.Keys)
-            {
-                component.RequiredParts[tag] = false;
-            }
-            _container.EmptyContainer(component.PartsContainer);
-            return;
-        }
-
-        if (!TryComp<TagComponent>(args.Used, out var tagComp))
-            return;
-
-        foreach (var (tag, val) in component.RequiredParts)
-        {
-            if (!val && _tag.HasTag(tagComp, tag))
-            {
-                component.RequiredParts[tag] = true;
-                _container.Insert(args.Used, component.PartsContainer);
-                break;
-            }
-        }
-
-        //check to see if we have all the parts
-        foreach (var val in component.RequiredParts.Values)
-        {
-            if (!val)
-                return;
-        }
-        Spawn(component.FinishedPrototype, Transform(uid).Coordinates);
-        Del(uid);
-    }
-}