feat: add non-persisted Async Payjoin support #793

Job	Run time
Rust fmt	15s
Build and test (stable, --features default)	1m 36s
Build and test (stable, --no-default-features)	1m 37s
Build and test (1.75.0, --no-default-features)	1m 41s
Build and test (stable, --all-features)	2m 29s
Build and test (1.75.0, --features default)	1m 48s
Build and test (1.75.0, --all-features)	2m 25s
	11m 51s

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