fix: include system messages in unread count

[myandrienko]

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

Before:

Screen.Recording.2024-09-04.at.12.43.32.mov

After:

Screen.Recording.2024-09-04.at.12.42.29.mov

[github-actions]

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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