when hashed urls are turned on, the _memory db has improperly long-lived cache expiry

[fgregg]

if hashed_urls are on, then a -000 suffix is added to the _memory database, and the cache settings are set just as if it was a normal hashed database.

in particular, this header is set:

cache-control: max-age=31536000

this is not appropriate because the _memory-000 database isn't really hashed based on the contents of the databases (see #1561).

Either the cache-control header should be changed, or the _memory db should have a hash suffix that does depend on the contents of the databases.

[fgregg]

this has been addressed by the datasette-hashed-urls plugin