feat: change Sourcer API to support sources where pending can not be … #41

Job	Run time
Build, Tag, and Push Image (examples/map-cat)	2m 14s
Build, Tag, and Push Image (examples/map-tickgen-serde)	2m 9s
Build, Tag, and Push Image (examples/mapt-event-time-filter)	2m 28s
Build, Tag, and Push Image (examples/reduce-counter)	2m 10s
Build, Tag, and Push Image (examples/sideinput)	2m 5s
Build, Tag, and Push Image (examples/sideinput/udf)	2m 35s
Build, Tag, and Push Image (examples/simple-source)	2m 17s
Build, Tag, and Push Image (examples/sink-log)	2m 31s
Build, Tag, and Push Image (examples/source-transformer-now)	2m 24s
Build, Tag, and Push Image (examples/batchmap-flatmap)	2m 6s
Build, Tag, and Push Image (examples/batchmap-cat)	2m 22s
	25m 21s

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