kunit: tool: add test counts to JSON output

kunit: tool: add test counts to JSON output

Add the test counts to the JSON output from kunit.py. For example:

...
"git_branch": "kselftest",
"misc":
{
    "tests": 2,
    "passed": 1.
    "failed": 1,
    "crashed": 0,
    "skipped": 0,
    "errors": 0,
}
...

To output the JSON using the following command:
./tools/testing/kunit/kunit.py run example --json

This has been requested by KUnit users. The counts are in a "misc"
field because the JSON output needs to be compliant with the KCIDB
submission guide. There are no counts fields but there is a "misc" field
in the guide.

Link: https://lore.kernel.org/r/20250516201615.1237037-1-rmoar@google.com
Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>