feat: adopt serialization generator v4 (field-side linkage, anchored timers) (#2586)

## Summary

Adopts ModernUO.Serialization 4.0.0 across the engine. Three commits, reviewable independently:

1. **Package + tool bump to 4.0.0** (`Server.csproj`, `UOContent.csproj`, `dotnet-tools.json`).
2. **Timers → `[DeserializeTimer]`** — the 8 drifting timers (BaseLight, TreasureMapChest, MarkContainer, FillableContainer, DeathRobe, DecayedCorpse, Corpse, BaseEscortable) now store their next tick as **anchored time**: server downtime no longer consumes the remaining delay, and idle-world saves are byte-stable. This changes their wire format, so each class bumps its serialization version with a `MigrateFrom` that replays the old delta-time read through the migration schema (the new `vN.json` files carry `@AnchoredTimer`; the old ones keep `@TimerDrift`, which the generator reads forever). The 2 wall-clock timers (Aquarium, FountainOfLife) keep their exact format via `wallClock: true` — no bump. Restart methods drop their `TimeSpan.MinValue` sentinel checks: v4 invokes them **only when a timer was actually running at save**.
3. **Linkage → field-side declarations** — 175 conversions across 25 files: `[SerializableFieldSaveFlag(order)]`/`[SerializableFieldDefault(order)]` become `[SaveFlag(nameof(...), nameof(...))]` on the field, and `[SerializableFieldChanged(order)]` becomes the `fieldChanged:` argument of `[SerializableField]`. **Wire-neutral: zero migration schemas changed.**

## Verification

- Solution builds with **0 errors, 0 warnings**; all three 4.0.0 packages verified indexed on nuget.org (no local feed needed).
- **835 + 708 tests green.**
- Generated output inspected: old-version content structs replay `ReadDeltaTime` (e.g. `V3Content.DecayTimerNext = reader.ReadDeltaTime()`), current versions write/read anchored time with the gated restart, and the wall-clock classes emit byte-identical `Write`/`ReadDateTime` framing.
- Schema tool run is committed (CI's `git diff --exit-code` schema check passes): exactly the 8 expected new `vN.json` files, nothing else touched.
- The conversion was scripted with a class-scoped resolver (order → same-class `[SerializableField(order)]`/`[SerializableProperty(order)]`); it planned 175/175 with zero ambiguities before applying.

## Notes

- New `MigrateFrom`s use the content structs' provided `XxxDelay` property, matching the pre-existing idiom in Corpse's and TreasureMapChest's older migrations.
- Follow-up candidate (separate PR, wire-neutral, any time): fold the ~150 eligible hand-written `[SerializableProperty]` setters (clamps, post-change side effects) down to `[SerializableField]` with `allowFieldChange`/`fieldChanged` hooks.

Projects/UOContent/Items/Misc/Corpses/Corpse.cs

@@ -86,7 +86,7 @@ public enum CorpseFlag
     OwnerWasAnimatedDead = 0x00000800
 }
 
-[SerializationGenerator(17, false)]
+[SerializationGenerator(18, false)]
 public partial class Corpse : Container, ICarvable
 {
     public static readonly TimeSpan MonsterLootRightSacrifice = TimeSpan.FromMinutes(2.0);
@@ -114,13 +114,37 @@ public partial class Corpse : Container, ICarvable
     [SerializableField(3, getter: "private", setter: "private")]
     private Dictionary<Item, Point3D> _restoreTable;
 
-    [TimerDrift]
     [SerializableField(4, getter: "private", setter: "private")]
+    [DeserializeTimer(nameof(DeserializeDecayTimer))]
     private Timer _decayTimer;
 
-    [DeserializeTimerField(4)]
     private void DeserializeDecayTimer(TimeSpan delay) => BeginDecay(delay);
 
+    private void MigrateFrom(V17Content content)
+    {
+        _restoreEquip = content.RestoreEquip;
+        _flags = content.Flags;
+        _timeOfDeath = content.TimeOfDeath;
+        _restoreTable = content.RestoreTable;
+        _looters = content.Looters;
+        _killer = content.Killer;
+        _aggressors = content.Aggressors;
+        _owner = content.Owner;
+        _corpseName = content.CorpseName;
+        _accessLevel = content.AccessLevel;
+        _guild = content.Guild;
+        _equipItems = content.EquipItems;
+        _hairItemId = content.HairItemId;
+        _hairHue = content.HairHue;
+        _facialHairItemId = content.FacialHairItemId;
+        _facialHairHue = content.FacialHairHue;
+
+        if (content.DecayTimerDelay != TimeSpan.MinValue)
+        {
+            DeserializeDecayTimer(content.DecayTimerDelay);
+        }
+    }
+
     [SerializableField(5, setter: "private")]
     private HashSet<Mobile> _looters;
 

Projects/UOContent/Items/Misc/Corpses/DecayedCorpse.cs

@@ -3,18 +3,25 @@ using ModernUO.Serialization;
 
 namespace Server.Items;
 
-[SerializationGenerator(2, false)]
+[SerializationGenerator(3, false)]
 public partial class DecayedCorpse : Container
 {
     private static TimeSpan _defaultDecayTime = TimeSpan.FromMinutes(7.0);
 
-    [TimerDrift]
     [SerializableField(0, getter: "private", setter: "private")]
+    [DeserializeTimer(nameof(DeserializeDecayTimer))]
     private Timer _decayTimer;
 
-    [DeserializeTimerField(0)]
     private void DeserializeDecayTimer(TimeSpan delay) => BeginDecay(delay);
 
+    private void MigrateFrom(V2Content content)
+    {
+        if (content.DecayTimerDelay != TimeSpan.MinValue)
+        {
+            DeserializeDecayTimer(content.DecayTimerDelay);
+        }
+    }
+
     public DecayedCorpse(string name) : base(Utility.Random(0xECA, 9))
     {
         Movable = false;