This creates a new postgres "domain" which is a subtype of some other type
(in this case, of INTEGER[]) with some constraints applied.
We use this to create a type which is explicitly an array of length 4.
This saves us from needing to repeat this constraint everywhere (which already led to one copy-paste error)
and is arguably clearer in intent.
We need this so that reverse sync reproduces these values correctly.
To handle this in the database, we have a composite type (dashed: boolean, value: timestamp).
Value is always valid and is equivalent to the old timestamp column,
but must be equal to start_time if dashed is true.
The only place we directly reference this column outside sheetsync is thrimshim, where we
always consider the value only.
This is more convenient for development since it's a standalone file that you can
apply without using the script, it also means we get syntax highlighting.