lib/protoparser/graphite: support parsing floating-point timestamp like Graphite does

Such timestamps are rounded to seconds like Carbon does.
See b0ba62a62d/lib/carbon/protocols.py (L197)

lib/protoparser/graphite/parser.go

@@ -98,12 +98,12 @@ func (r *Row) unmarshal(s string, tagsPool []Tag) ([]Tag, error) {
 	if err != nil {
 		return tagsPool, fmt.Errorf("cannot unmarshal value from %q: %w", tail[:n], err)
 	}
-	ts, err := fastfloat.ParseInt64(tail[n+1:])
+	ts, err := fastfloat.Parse(tail[n+1:])
 	if err != nil {
 		return tagsPool, fmt.Errorf("cannot unmarshal timestamp from %q: %w", tail[n+1:], err)
 	}
 	r.Value = v
-	r.Timestamp = ts
+	r.Timestamp = int64(ts)
 	return tagsPool, nil
 }
 

lib/protoparser/graphite/parser_test.go

@@ -113,6 +113,16 @@ func TestRowsUnmarshalSuccess(t *testing.T) {
 		}},
 	})
 
+	// Floating-point timestamp
+	// See https://github.com/graphite-project/carbon/blob/b0ba62a62d40a37950fed47a8f6ae6d0f02e6af5/lib/carbon/protocols.py#L197
+	f("aaa 1123 4294.943", &Rows{
+		Rows: []Row{{
+			Metric:    "aaa",
+			Value:     1123,
+			Timestamp: 4294,
+		}},
+	})
+
 	// Tags
 	f("foo;bar=baz 1 2", &Rows{
 		Rows: []Row{{