Unsafe instantiation of DateTime

[GrabYourPitchforks]

It is not safe to reinterpret_cast<> an arbitrary 64-bit value to a DateTime instance. Among other things, the .NET Framework and .NET Core runtimes do not guarantee that DateTime structure is backed by a single 64-bit integer field, and the DateTime type does not guarantee that all possible 64-bit representations are valid.

See offline comment for more details on how to do this safely and reliably.

Ref:

SafePayloadReader/System.Runtime.Serialization.BinaryFormat/Records/SerializationRecord.cs

Line 93 in cfb7ac5

return Unsafe.As<long, DateTime>(ref data);