v3.7.0

Added

• FixedSizeValueStringBuilder: a non-growing ref struct string builder backed by a caller-supplied buffer that never allocates on the heap. Appends are atomic and the first one that does not fit latches Overflowed, which ClearOverflow resets.
• FixedSizeValueStringBuilder.MoveToValueStringBuilder: hands the buffer and its content over to a ValueStringBuilder which can grow beyond the fixed capacity. The move copies nothing and rents nothing, and consumes the source so both builders can never write into the same memory.