tools: ynltool: add traffic distribution balance

tools: ynltool: add traffic distribution balance

The main if not only use case for per-queue stats today is checking
for traffic imbalance. Add simple traffic balance analysis to qstats.

 $ ynltool qstat balance
 eth0 rx 44 queues:
  rx-packets  : cv=6.9% ns=24.2% stddev=512006493
                min=6278921110 max=8011570575 mean=7437054644
  rx-bytes    : cv=6.9% ns=24.1% stddev=759670503060
                min=9326315769440 max=11884393670786 mean=11035439201354
  ...

  $ ynltool -j qstat balance | jq
  [
   {
    "ifname": "eth0",
    "ifindex": 2,
    "queue-type": "rx",
    "rx-packets": {
      "queue-count": 44,
      "min": 6278301665,
      "max": 8010780185,
      "mean": 7.43635E+9,
      "stddev": 5.12012E+8,
      "coefficient-of-variation": 6.88525,
      "normalized-spread": 24.249
    },
   ...

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20251107162227.980672-5-kuba@kernel.org
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>