Follow-up to #2729.
## Problem
At load, `ReadAnchoredTime` shifted **every** anchored value forward by the downtime, including values that were already in the past when the save started. That caused two problems.
**An expired deadline came back.** A deadline that passed 5 minutes before a 30-minute outage loaded 25 minutes in the future. For example:
- `Sheep.NextWoolTime`: a sheep that was ready to shear stopped being ready.
- `PlayerVendor.NextPayTime`: an overdue payment was pushed back.
- `BaseCreature.SummonEnd`, the spell fields' `End`, `TransientItem.Expiration`, and the ChampionSpawn times could move the same way.
**Records were rewritten for nothing.** The first save after every restart rewrote:
- stamps of things that had already happened: VirtueContext's `LastHonorUse`, `LastSacrificeGain`, the four `Last*Loss` stamps, and `Corpse.TimeOfDeath`
- every deadline that had expired long ago.
## Change
- **`IGenericReader.AnchoredTimeOrigin`** is the loaded save's start time.
- `GenericEntityPersistence` and `GenericPersistence` set it from `World.LoadedSaveStartTime`.
- `BufferReader`, `UnmanagedDataReader` and `BinaryFileReader` expose it.
- **`ReadAnchoredTime` returns any value at or before the origin exactly as saved.**
- A deadline still running at save start is shifted as before and keeps its remaining time.
- Readers without an origin keep the old behaviour.
- **This covers every anchored field, including generated ones.** Generated `[AnchoredDateTime]` fields call `reader.ReadAnchoredTime()`, so the one change covers all 26 generated fields as well as the manual reads. `[DeserializeTimer]` only restores timers that were running at save time, so it is unaffected.
- **The `[AnchoredDateTime]` section of `dev-docs/serialization.md` and the `WriteAnchoredTime` doc comment describe the new rule.**
## Behaviour change
Downtime now counts toward windows measured from a past stamp:
| Window | Length |
|---|---|
| Honor use | 5 minutes |
| Sacrifice gain | 1 day |
| Virtue atrophy | 7 days |
| Instanced corpse looting | 3 minutes |
A 30-minute outage makes a 7-day atrophy fire about 0.3% sooner. No format change.
## Tests
New tests in `AnchoredTimeTests`:
- A deadline running at save start keeps its remaining time.
- A deadline that passed before save start stays passed.
- A past stamp is not shifted.
- A value exactly at save start is not shifted.
`Server.Tests`: 845 passed. `UOContent.Tests`: 1140 passed.
## Summary
The save-stability infrastructure consumed by generator v3's `[AnchoredDateTime]`: anchored timestamps are written as **absolute values** and re-based once at load by the elapsed time since the save started — so downtime doesn't age them, and an unchanged entity serializes to identical bytes (the prerequisite for replacing delta-time encodings, which rewrite every entity on every save).
## Design
- **`WriteAnchoredTime` / `ReadAnchoredTime`** on `IGenericWriter`/`IGenericReader`. The read side applies the reader's `AnchoredTimeShift`; `Min/MaxValue` sentinels pass through unshifted, and shifts saturate instead of overflowing.
- **`World.SaveStartTime`** is stamped the moment the world freezes for a snapshot — one anchor for the entire save, no per-persistence skew.
- **idx v5**: the anchor ticks sit in the header right after the version. The anchor travels with the file it re-anchors, so a single idx+bin pair restored from a backup is self-describing, and anchor presence is guaranteed by the same version gate as the record format — there is no separate anchor file to lose.
- **The shift rides the reader instance** (`BufferReader`, `UnmanagedDataReader`, `BinaryFileReader` delegating), not a static — parallel per-persistence loads and ad-hoc restores each see their own file's anchor. idx v4 and older read with a zero shift.
## Scope
Behavior-neutral: nothing serializes anchored values yet (`Item.DecayResetTime` and the `[DeltaDateTime]` field migrations come separately, with their own version bumps). Saves written from this branch are idx v5; loading v4/v3 saves is unchanged and remains pinned by the existing hand-written-header tests.
## Testing
- Unit round-trips: exact with zero shift, shifted read, sentinel passthrough, saturation, Local→UTC normalization.
- End-to-end through the real worker/segment-log pipeline: an anchored timestamp re-bases across a simulated two-hour downtime via the idx v5 header.
- Full suites green: Server.Tests 835/835, UOContent.Tests 708/708 (including the existing v4/v3 idx loading tests).
### Summary
Updates the serialization strategy to use `MemoryMappedFile` instead of thick buffers. This has the benefit of being on-par with the current implementation (based on hardware/OS), however won't incur the double-memory issue.
> [!Important]
> **Developer Note**
> The `BinaryFileWriter` and `BinaryFileReader` has been removed in favor of `MemoryMapFileWriter` and `UnmanagedDataReader`
