Optimize TagReader/TagWriter

[ForeverZer0]

The TagReader and TagWriter class still use the naive and legacy method of BitConverter.GetBytes paired with Array.Reverse to get the correct byte-order.

Replace all these method calls with the use of stackalloc spans and employ BinaryPrimitives methods to read/write in the appropriate endian. This will make them free of any heap-allocations in additional to being computationally less expensive.