Stop JsonFormatter from encoding INF and NaN as 0 - #2078

JsonFormatter logs INF, -INF and NAN as 0:

$logger->warning('ratio', ['ratio' => INF, 'avg' => NAN]);
// {"message":"ratio","context":{"ratio":0,"avg":0},...}

JSON has no representation for these values. json_encode() fails on them, and because Utils::DEFAULT_JSON_FLAGS includes JSON_PARTIAL_OUTPUT_ON_ERROR, each one is replaced with 0. That reads like a real measurement, so the log ends up misleading rather than visibly broken.

NormalizerFormatter::normalize() already maps these to the strings 'INF', '-INF' and 'NaN' (from #523), and LineFormatter gets that for free. JsonFormatter overrides normalize() and returns scalars untouched, so it missed out. This PR hands non-finite floats to the parent, so JsonFormatter gives the same output as the other formatters. All other scalars are still returned as they are.

I added a JsonFormatter test covering INF, -INF, NAN, a nested INF, and a normal float. It fails on main with 0 is identical to 'INF'. The full PHPUnit suite and PHPStan pass.