prepare_connection() plugin hook

[simonw]

Splitting off an issue for prepare_connection() since Alex got the PR in seconds before I shipped 3.34!

Originally posted by @simonw in #567 (comment)

[simonw]

Alex built this in:

• feat: Implement a prepare_connection plugin hook #573

[simonw]

Documentation: https://sqlite-utils.datasette.io/en/latest/plugins.html#prepare-connection-conn

[simonw]

Just tried this out by adding the example from the docs to my sqlite-utils-hello-world plugin and running:

sqlite-utils install -e ../sqlite-utils-hello-world 

Obtaining file:///Users/simon/Dropbox/Development/sqlite-utils-hello-world
...

Then:

sqlite-utils memory "select hello('simon')"

[{"hello('simon')": "Hello, simon!"}]

Also:

>>> import sqlite_utils
>>> db = sqlite_utils.Database(memory=True)
>>> list(db.query("select hello('simon')"))
[{"hello('simon')": 'Hello, simon!'}]
>>> db2 = sqlite_utils.Database(memory=True, execute_plugins=False)
>>> list(db2.query("select hello('simon')"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/simon/Dropbox/Development/sqlite-utils/sqlite_utils/db.py", line 494, in query
    cursor = self.execute(sql, params or tuple())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/simon/Dropbox/Development/sqlite-utils/sqlite_utils/db.py", line 512, in execute
    return self.conn.execute(sql, parameters)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
sqlean.dbapi2.OperationalError: no such function: hello