Use embed=body mode for stream feed iterators to support $all and system streams

[Copilot]

StreamFeedIterator used readEventBatch() to fetch events individually by URL. System events (e.g. $ProjectionCreated) return null content at their individual URLs, causing silent skips. The $all stream was similarly affected.

The fix leverages EntryEmbedMode::BODY when opening feeds, embedding event data directly in feed entries — eliminating the N+1 request pattern and working for all stream types.

Changes

• StreamFeedIterator — opens feeds with EntryEmbedMode::BODY, reads embedded events from entries instead of calling readEventBatch()
• Entry — added ?Event $embeddedEvent constructor param and getEmbeddedEvent() accessor
• EntryDenormalizer — accepts EventDenormalizer, extracts embedded event during entry denormalization
• EventDenormalizer — relaxed supportsDenormalization (no longer requires data key), handles null data (system events) and JSON-string data (embed=body format) via new decodeField() helper
• EventStoreFactory / SerializerFactory — adjusted instantiation order since EntryDenormalizer now depends on EventDenormalizer

Before/After

// Before: silently skips system events and $all entries
$iterator = $eventStore->forwardStreamFeedIterator(rawurlencode('$all'));
iterator_count($iterator); // Undercounts — many events skipped

// After: all events including system events are yielded
$iterator = $eventStore->forwardStreamFeedIterator(rawurlencode('$all'));
foreach ($iterator as $key => $entryWithEvent) {
    $entryWithEvent->getEvent()->getType(); // e.g. "$ProjectionCreated"
    $entryWithEvent->getEvent()->getData(); // [] for system events without data
}