fix(database) :: test the connection pool hooks and the retry backoff

[81reap]

on_connect.sql and on_reset.sql are documented in configuration.md but are not covered by any tests.

The retry test runs on a paused clock, so it asserts that each retry waits five seconds and that the loop then gives up.

discovered by #1396

SQLPage/configuration.md

Lines 239 to 280 in 6d32b40

	### Connection initialization scripts
	SQLPage allows you to run a SQL script when a new database connection is opened,
	by simply creating a `sqlpage/on_connect.sql` file.
	This can be useful to set up the database connection for your application.
	For instance, on postgres, you can use this to [set the `search path` and various other connection options](https://www.postgresql.org/docs/current/sql-set.html).
	```sql
	SET TIME ZONE 'UTC';
	SET search_path = my_schema;
	```
	On SQLite, you can use this to [`ATTACH`](https://www.sqlite.org/lang_attach.html) additional databases.
	```sql
	ATTACH DATABASE '/path/to/my_other_database.db' AS my_other_database;
	```
	(and then, you can use `my_other_database.my_table` in your queries)
	You can also use this to create *temporary tables* to store intermediate results that are useful in your SQLPage application, but that you don't want to store permanently in the database.
	```sql
	CREATE TEMPORARY TABLE my_temporary_table(
	my_temp_column TEXT
	);
	```
	### Connection cleanup scripts: `on_reset.sql`
	SQLPage allows you to run a SQL script after a request has been processed,
	by simply creating a `sqlpage/on_reset.sql` file.
	This can be useful to clean up temporary tables,
	rollback transactions that were left open,
	or other resources that were created during the request.
	You can also use this script to close database connections that are
	in an undesirable state, such as being in a transaction that was left open.
	To close a connection, write a select statement that returns a single row
	with a single boolean column named `is_healthy`, and set it to false.