feat: Amortize the cost of database setup in postgres through the use of template databases.

[DanCardin]

Today we create a brand new test database for each test, it's completely empty, and then we populate the database with ordered_actions to fill it with the DDL/data we need in the tests.

The idea is that we make use of postgres' template database feature which replicates the state of a database from another database (which happens always, just your default template template1 is empty by default). We avoid tons of python/sqlalchemy stuff, and presumably postgres is optimized to do what it does quickly.

Large test suite

• Before: 1204 passed, 3 errors in 1458.88s (0:24:18) (funnily, i got errors on the head version, didn't look into why)
• After (Statements, as-is): 1207 passed in 433.54s (0:07:13)
• After (Statements -> StaticStatements): 1207 passed in 383.83s (0:06:23)

The above is with -n 4 parallelism. the numbers get better as you increase parallelism. I stopped the original suite after 40 mins without parallelism, whereas with this PR it took 17m (faster than the parallelized pre-PR version)

For pytest-mock-resources' own test suite, it's essentially the same or slightly slower overall because there necessarily tends to be close to a 1-to-1 correspondence between each test and its fixture to test PMR's fixture args/features.

[luke-mino-altherr]

i'm assuming youll fix tests?

[DanCardin]

yea, it was all passing a few moments ago, i added a new test and broke some stuff.