kvserver: print msstw stats in TestMultiSSTWriterInitSST

There seem to be many overlapping stats, this is likely worth
cleaning up at some point, but for now simply note what values
result in the test as is.

Author: tbg

pkg/kv/kvserver/replica_sst_snapshot_storage_test.go

@@ -302,6 +302,8 @@ func TestMultiSSTWriterInitSST(t *testing.T) {
 
 	var buf redact.StringBuilder
 
+	_, _ = fmt.Fprintf(&buf, "writeBytes=%d sstSize=%d dataSize=%d\n", msstw.writeBytes, msstw.sstSize, msstw.dataSize)
+
 	for i := range fileNames {
 		name := fmt.Sprintf("sst%d", i)
 		require.NoError(t, storageutils.ReportSSTEntries(&buf, name, actualSSTs[i]))

pkg/kv/kvserver/testdata/echotest/TestMultiSSTWriterInitSST

@@ -1,5 +1,6 @@
 echo
 ----
+writeBytes=4740 sstSize=4872 dataSize=132
 >> sst0:
 rangedel: /Local/RangeID/0/{r""-s""}
 rangekeydel: /Local/RangeID/0/{r""-s""}