audit: carry the two recovered idle fields into the python field list

bench-audit_test's drift guard caught its own list falling behind record.rs the
moment CellMemory started carrying idle_static and idle_growth_rate_mib_per_min
- which is exactly what that guard is for: every check built on this list would
otherwise have been silently blind to two fields that had just stopped being
dropped on the floor.

Unlike the shape fields, these are ordinary numeric metrics and are held to 'a
served cell publishes a number'.

Author: MattJackson

bench-audit.py

@@ -336,6 +336,12 @@ def check_ttft_percentiles_are_ordered(name, c):
         # check_no_bare_absence's "a served cell publishes a number", which is why that check reads
         # SHAPE_FIELDS below and lets a reasoned absence stand.
         "shape", "idle_shape",
+        # The idle window's own verdict and its fitted slope. The memory group measured both on every
+        # served cell and CellMemory had nowhere to put them, so they reached the artifact as neither
+        # a number nor a null - a missing key, invisible to every check built on this list. They are
+        # ordinary numeric metrics (a settled idle window publishes 1.0 and its slope), so unlike the
+        # shape fields they ARE held to 'a served cell publishes a number'.
+        "idle_static", "idle_growth_rate_mib_per_min",
     ],
 }