Before this change, the only distinction between a timestamp and a TID was
the presence of the decimal separator, ".". As a result, a timestamp
mistakenly provided without a decimal separator would be interpreted as a
TID, which will be somewhere in January 1900 (as TIDs are 64bits with much
finer accuracy than timestamps). When used to truncate a database, and in
the absence of sanity checks, this would simply wipe the database.

So, instead of just relying on a decimal separator, require a longer
string. Make it a prefix for readability. Also, TIDs are more niche than
timestamp, require them to have a mark, and do not require anything from
timestamps.