In-memory StepExternalByteStore. Used by tests and as a degenerate store when the caller wants windowed accounting without real external storage.
Construct this around a byte array (not copied).
The backing bytes.
Total size of the stored byte sequence.
The byte length.
Read a range as a standalone copy.
Absolute offset of the first byte to read.
Number of bytes to read.
The bytes.
In-memory StepExternalByteStore. Used by tests and as a degenerate store when the caller wants windowed accounting without real external storage.