fix: include system messages in unread count

[myandrienko]

The client should include system messages in the unread count, like all other SDKs do.

Before:

https://github.com/user-attachments/assets/11a59968-1b3b-4528-9cbf-1040abedb49b

After:

https://github.com/user-attachments/assets/2c85ff18-8c8d-44a0-83ae-e8e8d863ab40

[github-actions[bot]]

Size Change: -64 B (-0.02%)

Total Size: 425 kB

Filename	Size	Change
dist/browser.es.js	92.2 kB	-14 B (-0.02%)
dist/browser.full-bundle.min.js	54 kB	-12 B (-0.02%)
dist/browser.js	93.3 kB	-13 B (-0.01%)
dist/index.es.js	92.2 kB	-13 B (-0.01%)
dist/index.js	93.3 kB	-12 B (-0.01%)

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