Derive per NUMA node DRAM latency on AMD (#598)

Summary:

The amd_l3 sampled-latency counters are per CCX, and the Dram_Near data source
already means "this CCX's own NUMA node". The shared uncore path sums every
CCX instance into a single host sample before any average is taken, so the node
breakdown is lost and only a host-wide latency is available.

Read the `L3DramLat` group a second time through the new keyed API, which
preserves the device key. The key carries the servicing CPU, and a CCX belongs
to exactly one NUMA node, so the values can be bucketed per node and published
as `L3DramLat::node<N>` metric frames alongside the untouched host frame.
`calcAvgL3ToNearDramLatNanoSecForNode()` then reads a node's frame with the
existing latency math.

Notes:
- The per node average sums the accumulators and the request counts separately
  before dividing, so busier CCXs weigh proportionally. Averaging the per-CCX
  ratios would be wrong.
- The node topology comes from sysfs once at configure time; it is fixed for
  the lifetime of the boot. A memory-only node (CXL) has no CPUs and so never
  becomes an empty bucket.
- The host path, its metric names, and the perf event count are unchanged, so
  the shipped `l3_to_*_dram_lat_avg_ns` keys are unaffected.
- `saveArchSpecificMetricFrames()` is a no-op hook on the base, so Intel and
  ARM are unaffected.

Differential Revision: D116837219

Author: abhiShedge

hbt/src/perf_event/tests/MockPerUncoreCountReader.h

@@ -38,6 +38,11 @@ class MockPerUncoreCountReader : public PerUncoreCountReader {
       readPerPerfEventsGroup,
       (),
       (const, override));
+  MOCK_METHOD(
+      (std::optional<std::map<int, ReadValues>>),
+      readPerPerfEventsGroupKeyed,
+      (),
+      (const, override));
   MOCK_METHOD(
       (std::map<int, ReadValues>),
       readPerPerfEventsGroupOnCpu,