WriteAnchoredTime stores the absolute value; ReadAnchoredTime re-bases it
by the elapsed time since the loaded save started, so downtime does not
age it and an unchanged value serializes to identical bytes. Min/MaxValue
pass through unshifted and shifts saturate instead of overflowing. The
shift rides the reader instance, so parallel per-persistence loads and
single-file restores each see their own file's anchor.
World.SaveStartTime is stamped the moment the world freezes for a
snapshot - one anchor for the whole save - and written into the idx v5
header. Loading an idx v5 computes the shift and applies it to that
persistence's bin readers; v4 and older carry no anchor and read with a
zero shift, which existing hand-written-header tests already pin.
Nothing serializes anchored values yet; field conversions follow
separately. Covered by unit round-trip tests and an end-to-end
persistence test that re-bases across a simulated two-hour downtime.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
### 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`
