Replaces #2839 and refs #2838

Peewee is compatible with MariaDB Server. Add clarifying notes in the
documentation, including logo, etc.

Testing
```
docker run -d -p 3306:3306 --name mariadb_container -e MYSQL_ROOT_PASSWORD=password mariadb
```

```
>>> from peewee import MySQLDatabase
>>> database = MySQLDatabase('information_schema', user='root', password='password', host='127.0.0.1', port=3306)
>>> database.connect()
True
>>> version_query = database.execute_sql('SELECT VERSION()')
>>> print(version_query.fetchone()[0])
11.3.2-MariaDB-1:11.3.2+maria~ubu2204
>>> database.close()
True
```

Add docs clarifying compatibility with MariaDB

Warning: this set of functions requires a good deal of care to use correctly.

[skip ci]

Also run postgres-specific tests against the psycopg3 driver.

Also ensure present for CI.

Also fixes some instances where parameterization of values is not
supported. A surprising one was IS/IS NOT NULL where "NULL" is not
allowed to be parameterized (None converts to NULL with psycopg2).
We'll just explicitly specify the sql literal NULL for these
comparisons. This change affects the other implementations as well.

Python's list() function may trigger len() multiple times, in addition to
iter(). Adding a bool override avoids these extraneous len calls.

Fixes #2871