Previously, we applied replacements to our schema definitions
to make them compatible with both SQLite and Postgres backends,
as the files were not fully compatible with either.
With this change, the only replacement required for SQLite has
been moved to the generator script. This adjustment ensures
compatibility by enabling auto-incrementing primary keys that
are treated as 64-bit integers by sqlc.
This commit attempts to fix some issues with the invoice store's schema that we
couldn't foresee before the implementation was finished. This is safe as the
schema has not been instantiated yet outside of unit tests. Furthermore the
commit updates invoice store SQL queries according to fixes in the schema as
well as to prepare the higher level implementation in the upcoming commits.
