Move priority queue to pq package; improve docs.

circ/lib.go

@@ -1,6 +1,7 @@
+// Package circ implements a circular FIFO buffer.
 package circ
 
-// B is a generic, non-concurrent circular FIFO buffer.
+// B is a circular FIFO buffer.
 type B[T any] struct {
 	buf  []T
 	len  int