Migrate read-state request bodies to generated models

[gpunto]

Goal

Migrate the read-state request bodies (markRead, markUnread) to generated models. Part of the incremental OpenAPI model migration.

Part of AND-1291

Implementation

• Add generated internal MarkReadRequest and MarkUnreadRequest in network.models; delete the hand-written ones. Point ChannelApi/MoshiChatApi/tests at them.
• Field names move to camelCase with @Json names preserved (message_id -> messageId, message_timestamp -> messageTimestamp, thread_id -> threadId), so the wire format is unchanged; only positional/named args at the call sites change.
• markAllRead sends no body, so there is no MarkChannelsReadRequest to migrate here.

Testing

• Project-wide spotlessApply, apiDump (no API drift), detekt, and testDebugUnitTest all pass.
• Verified on device: markMessageRead -> 200, markUnread -> 200.

[github-actions]

PR checklist ✅

All required conditions are satisfied:

• Title length is OK (or ignored by label).
• At least one pr: label exists.
• Sections ### Goal, ### Implementation, and ### Testing are filled, or the PR is bot-authored.
• An issue is linked (Linear ticket or GitHub issue), or the PR is bot-authored.

🎉 Great job! This PR is ready for review.

[github-actions]

SDK Size Comparison 📏

SDK	Before	After	Difference	Status
stream-chat-android-client	5.93 MB	5.93 MB	0.00 MB	🟢
stream-chat-android-ui-components	11.20 MB	11.19 MB	-0.01 MB	🚀
stream-chat-android-compose	12.66 MB	12.67 MB	0.00 MB	🟢

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
80.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud