Three-layer fix silences PHP 8.2 deprecation noise in WP-CLI JSON output

A multi-site maintenance tool failed when `wp plugin list --format=json` returned mixed output due to PHP 8.2+ deprecation warnings leaking into stdout. The root cause was older WP-CLI 2.x using dynamic properties, with `display_errors` sending warnings to stdout instead of stderr. The fix uses three layers: `WP_CLI_PHP_ARGS` to suppress warnings, output filtering to strip non-JSON lines, and fallback parsing to handle partial JSON.