BaseMsgPackReader

Copies the non-dropped Bytes in the current buffer to the start of either the current buffer, or a newly-allocated larger buffer if necessary.

Used to ensure that byteents up to until are available to read; returns whether or not we have read off the end of the input.

In the fast path, when until is less than the lastIdx we have buffered, there is no work to do and we return false.

In the slow path, when until is more than lastIdx, we then run growBuffer to grow the buffer if necessary, and then readDataIntoBuffer to populate it. readDataIntoBuffer returns a newDone value to indicate whether we have read off the end of the input or not.

Note that for some subclasses, growBuffer may be a no-op when we already know we have reached the end of input.

Used to ask for data up to a certain index, as a best effort (unlike requestUntil), returning the "safe index" which it was actually able to fetch data for. This is used so the caller can use the safe index to know how far it is able to run getByteUnsafe calls without further checks, improving performance over calling getByteSafe every time which performs additional checks and logic