Added non-atomic SPI connection

[YohDeadfall]

Here's my take on making non-atomic SPI connections, but it lacks tests as I don't understand how to properly make them without dealing with portals directly. If I'm not wrong there were tests using a client to issue requests to the server with the required extensions, so it should be like that then.

[eeeebbbbrrrr]

What's the use case for non-atomic SPI?

[YohDeadfall]

It's used primarily if not only by language handlers which take that information from the current call. The problem I see is that the native API allows opting-in into non-atomic connections using SPI_connect_ext, but the provided implementation is less flexible, but more sound because with atomic connections no transaction control functions are allowed.

[dpxcc]

What's the use case for non-atomic SPI?

Non-atomic SPI can be quite useful for stored procedures and background workers

By the way, I'm curious why pgrx doesn't offer more native support for stored procedures

[YohDeadfall]

By the way, I'm curious why pgrx doesn't offer more native support for stored procedures

It's purely contributor based now, no company owns it or sponsors it.