fix(formatters): strip duplicate keys from Extra Data section

[Naoray]

Summary

• ExtraFormatter now excludes the same dedicated-section keys that ContextFormatter already strips (exception, environment, request, route, route_summary, user, queries, job, command, outgoing_requests, session, livewire, livewire_originating_page, inertia)
• Uses Illuminate\Support\Arr::except() for consistency with ContextFormatter
• Added tests verifying that dedicated-section keys are excluded and that the formatter returns an empty string when only excluded keys are present

Closes #32

Test plan

• Existing ExtraFormatterTest tests pass unchanged
• New test: it excludes keys that have dedicated sections -- verifies all 14 keys are stripped while custom keys remain
• New test: it returns empty string when all keys are excluded -- verifies empty output when only section keys exist
• Full test suite passes (281 tests, 878 assertions)

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