Prior to this patch '0' would be dropped as the config values default
to 0. Some json values are hex and the string '0' wouldn't match '0x0'
as zero. Add a more robust is_zero test to drop these event terms.

When encoding numbers as hex, if the number is between 0 and 9
inclusive then don't add a 0x prefix.

Update test expectations for these changes.

On x86 this reduces the event/metric C string by 58,411 bytes.
Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Edward Baker <edward.baker@intel.com>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240131201429.792138-1-irogers@google.com