Add default pragma values for newly opened databases

[noteflakes]

Some sensible defaults here: https://gcollazo.com/optimal-sqlite-settings-for-django/

# define pragmas manually
Extralite.default_pragmas = {
  ...
}

# one possibility for letting extralite manage it
Extralite.modern_settings!

# another, somewhat better possibility:
require 'extralite/sensible_default_pragmas'

[fractaledmind]

Minus the temp_store setting, these are exactly the defaults that @oldmoe and I recommend and are now default in Rails:

https://fractaledmind.github.io/2023/09/07/enhancing-rails-sqlite-fine-tuning/
rails/rails#49349