readDoubleBe
Reads a 64-bit IEEE 754 double in big-endian order starting at offset.
The eight bytes are decoded as with readLongBe and reinterpreted through Double.fromBits, so the exact bit pattern is preserved, including NaN payloads written by writeDoubleBe.
Return
the decoded value.
Parameters
offset
the index of the first byte to read.
Throws
if offset is negative or offset + 8 exceeds the array size.