Fix cgroup jobmetric formatter to always return properly formatted

strings, add typing to specify, instead of casting this higher in the
stack.

lib/galaxy/job_metrics/__init__.py

@@ -107,7 +107,7 @@ def raw_to_dictifiable(raw_metric: RawMetric) -> DictifiableMetric:
                 safety = DEFAULT_SAFETY
             return DictifiableMetric(
                 title,
-                str(value),
+                value,
                 str(metric_value),
                 metric_name,
                 metric_plugin,

lib/galaxy/job_metrics/instrumenters/cgroup.py

@@ -114,18 +114,18 @@
 
 
 class CgroupPluginFormatter(formatting.JobMetricFormatter):
-    def format(self, key, value):
+    def format(self, key: str, value: Any) -> formatting.FormattedMetric:
         title = TITLES.get(key, key)
         if key in CONVERSION:
-            return title, CONVERSION[key](value)
+            return formatting.FormattedMetric(title, CONVERSION[key](value))
         elif key.endswith("_bytes"):
             try:
-                return title, nice_size(value)
+                return formatting.FormattedMetric(title, nice_size(value))
             except ValueError:
                 pass
         elif isinstance(value, (decimal.Decimal, numbers.Integral, numbers.Real)) and value == int(value):
             value = int(value)
-        return title, value
+        return formatting.FormattedMetric(title, str(value))
 
 
 class CgroupPlugin(InstrumentPlugin):