Improve conversion of bytes to human readable string

Fixes issues like showing 0 MiB when the value is just slightly less then 1 MiB.

tests/pglabtests/tst_HumanReadableBytes.cpp

@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+#include <gmock/gmock-matchers.h>
+#include "PrintTo_Qt.h"
+
+#include "utils/HumanReadableBytes.h"
+
+TEST(HumanReadableBytesTest, bytes7)
+{
+    auto s = HumanReadableBytes(7);
+    ASSERT_EQ("7 B", s);
+}
+
+TEST(HumanReadableBytesTest, bytes1023)
+{
+    auto s = HumanReadableBytes(1023);
+    ASSERT_EQ("1023 B", s);
+}
+
+TEST(HumanReadableBytesTest, bytes1k)
+{
+    auto s = HumanReadableBytes(1024);
+    ASSERT_EQ("1.00 kiB", s);
+}