Provide extensions to read/write unsigned byte arrays

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There are several extensions allowing to read/write byte arrays, as well as extensions operating on unsigned numbers, but there are no extensions working with unsigned byte arrays.

It's always an option to convert a regular byte array to an unsigned one, but doing so adds unnecessary overhead.

We should consider providing extensions to read and write unsigned byte arrays directly.

The same is true for ByteStrings (at least, for their construction).

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That part is wrong in presence of asByteArray/asUByteArray functions:

It's always an option to convert a regular byte array to an unsigned one, but doing so adds unnecessary overhead.

There were no demand for this functions in form of questions / additional requests / comments in this issue, so for now I'm closing it. The decision could always be reconsidered.