Merge pull request #1421 from ydb-platform/async-create-session

internal/pool async create and close item

Author: asmyasnikov

internal/pool/errors.go

@@ -8,4 +8,5 @@ var (
 	errClosedPool     = errors.New("closed pool")
 	errItemIsNotAlive = errors.New("item is not alive")
 	errPoolIsOverflow = errors.New("pool is overflow")
+	errNoProgress     = errors.New("no progress")
 )