Add proper span handling to factories through extension trait #641

Job	Run time
benches	3m 36s
Clippy	1m 6s
docs	1m 21s
rustfmt	13s
Run the default tests	3m 14s
Test ractor without span propogation	3m 19s
Test ractor with the `cluster` feature	3m 25s
Test ractor with the `blanket_serde` feature	3m 23s
Test ractor_cluster	3m 15s
	22m 52s

Provide feedback