## Why
Delta world saves re-serialize an entity only when it has been marked dirty. An audit of the generated classes found three ways serialized state changes without a mark; this PR closes the ones that do not need a new generator package.
## What
- **Custom `[SerializableProperty]` setters mark dirty.** Twelve hand-written setters assigned their backing field without `this.MarkDirty()`. `PlagueBeastLord.OpenedBy` was an auto-property carrying the attribute with no backing field at all; it is now a generated field with the same name, order and command-property exposure.
- **Generated sub-objects are linked to their owner.** Without a `[DirtyTrackingEntity]` member the generator emits setters that mark nothing. Eight entity-owned sub-objects now carry the link and receive the owner through the constructor the generator calls: `BOBFilter` (owner is `IEntity`: a `PlayerMobile` or a `BulkOrderBook`), `BOBLargeSubEntry`, `PuzzleChestSolution` and `PuzzleChestSolutionAndTime`, `TalismanAttribute` (the random factories now take the talisman), `VendorItem`, `PlayerBBMessage`, `RaffleEntry`, `ShardPollOption`. Migration schemas were regenerated with the pinned tool; the only change is the value rule argument becoming `DeserializationRequiresParent`.
- **BaseVendor uses the generator; restock amounts are no longer persisted.** The only state it wrote was which buy entries had grown restock amounts, packed by index into the live `SBInfos` tables. Restock is transient now and rebuilds on load; version 1 records are read and discarded through the legacy path. Every vendor subclass now serializes through a generated chain.
## Generator 4.1.0
This PR adopts SerializationGenerator 4.1.0 (modernuo/SerializationGenerator#55): SG3019/SG3020 diagnostics, `[VolatileSerializedState]`, `StopXxx()` timer helpers, and owner-constructor preference for sub-objects (so dictionary values are constructed with their owner; the 4.0.0 relink fallback is gone). `PlayerVendor.v3.json` gains `DeserializationRequiresParent` for its `VendorItem` values so the migration content struct constructs them with their vendor.
SG3019 is an error under `TreatWarningsAsErrors` and generator diagnostics ignore pragmas, so the five contexts that live in whole-file player-keyed persistences (`ChampionTitle`, `ChampionTitleContext`, `MurderContext`, `VirtueContext`, `JailRecord`) now carry a `[DirtyTrackingEntity]` link to their `PlayerMobile`, which is where they will live once those blobs move onto the player record. `JailSystem.EmptyRecord` keeps a null player (`[CanBeNull]`). `ChampionTitle` needs both a context and a player constructor because the generator resolves the rule against the containing type but emits the call with the parent field; a comment in the file records this.
## Wire format
Unchanged. No version bumps except `BaseVendor` 1 to 2 (which now writes nothing of its own). Schema diffs are rule-argument only (`DeserializationRequiresParent`).
## Testing
Server.Tests 848 passed, UOContent.Tests 759 passed.
## 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.
* Adds `SerializationProperty` - This will generate the private variable for serialization. Also provides an option `useField` to specify your own. Example:
```cs
[SerializationProperty(0, useField: nameof(_resource)]
```
