One stored cell: the raw value bytes, as text.
Bigtable keeps a timestamped version history per cell and returns the
versions newest first (measured). This adapter reads version [0] and
carries no timestamp: cell versioning has no counterpart in the portable
data-access contract, so a facade that produced one would be producing a
value nothing reads.
readonly
value: string
The cell value, as the text the adapter's value codec wrote.