CLI metrics table renders blank cells for counters and histograms #221

MetricsReporter only knows how to render Metrics.Timer. Both table paths in
cli/src/main/java/io/github/open_policy_agent/opa/cli/MetricsReporter.java
test instanceof Metrics.Timer and leave everything else as the empty string:

• printSingleMetricsTable (lines 39-43 and 56-61) initialises String value = ""
  and only fills it in for a timer.
• printStatisticalMetricsTable (line 74) collects values only for timers, so
  non-timer metrics are dropped from that table entirely.

Until #216, SimpleMetrics.all() returned only timers, so this was unreachable.
That PR makes all() return counters and histograms too, so a metric registered
via Metrics.counter(...) or Metrics.histogram(...) now reaches the reporter and
prints as a row with a blank cell under TIME.

Nothing in the repo registers a counter or histogram yet, so this is not visible
in normal CLI use today — it only shows up for an embedder that registers one on
the Metrics instance passed to an evaluation. It seemed better as a follow-up
than as scope added to #216.

Suggested fix

Handle the other two types the way MetricsPrinter already does
(opa-evaluator/src/main/java/io/github/open_policy_agent/opa/metrics/MetricsPrinter.java:78-87):
counters print their integer value, histograms explode into one row per stat.
The TIME column header also stops being accurate once non-timers can appear.