mutation_fragment.hh: move operator<<(partition_region) to position_in_partition.hh

Where its definition lives.

mutation_fragment.hh

@@ -525,7 +525,6 @@ inline position_in_partition_view partition_end::position() const
     return position_in_partition_view(position_in_partition_view::end_of_partition_tag_t());
 }
 
-std::ostream& operator<<(std::ostream&, partition_region);
 std::ostream& operator<<(std::ostream&, mutation_fragment::kind);
 
 

position_in_partition.hh

@@ -80,6 +80,8 @@ enum class partition_region : uint8_t {
     partition_end,
 };
 
+std::ostream& operator<<(std::ostream&, partition_region);
+
 class position_in_partition_view {
     friend class position_in_partition;