[feature] - concurrent query excecutors

[ChuckHend]

The single background worker process currently polls on an interval. This is unlikely to scale when the number of queries in the queue grows. Build a feature to configure the number of concurrent worker processes, or implement some sort of concurrency in the background worker. Note, the background worker itself might be tricky to implement as a Rust async function, but we aren't using the SPI so maybe there is a work around.