Fixed PostgresDriver (for jvmMain) to correctly make use of the connection pool.

[smyrgeorge]

I just made the appropriate changes.
Before the code was using just a single connection. 😄

[moreirasantos]

Thank you for your implementations!

I haven't noticed that r2dbc wasn't using a pool, so I'll have to test the before and after when I can. Please keep in mind that I'll most likely be away from keyboard for a few days.
Cheers!

[smyrgeorge]

I realized that isn't using the connection pool because I was reviewing the whole codebase in order to support transactions.
In a future PR I can provide the implementation.
I think, for now, we should be more "focused" on creating a bit more "stable" interfaces/wrappers in order to support more features (like transactions).
I think the r2dbc codebase can guide us a bit on that.
Then in the future we can change the underlying engines.
For instance for the native part we could use sqlx (rust lib) through c bindings (same as we do now with libpq).

Let me know about the comments above 😄

[moreirasantos]

Indeed, that was my idea when adding r2dbc (having something to compare to). One thing that jumps out right away for example, is sending multiple SQL statements in one go, which r2dbc already supports and this interface kind of hides/limits that.
Thank you again :)

[smyrgeorge]

Sure! So, I'll do the changes later on and in the next days I'll provide the implementation for the transactions.
At least I'll try to 😄

[smyrgeorge]

Hello! I just made the changes according to the conversation above.
Please feel free to review and then close the PR 😄