Migrate poll write request bodies to generated models

[gpunto]

Goal

Migrate the poll write request bodies (createPoll, updatePoll, createPollOption, updatePollOption) to the generated CreatePollRequest, UpdatePollRequest, CreatePollOptionRequest, UpdatePollOptionRequest, PollOptionInput, and PollOptionRequest network models. Unblocked by the CHA-4436 backend fix that tags the poll request custom field.

Part of AND-1291

Implementation

• Add the 6 generated internal poll write-request models; remove the hand-written CreatePollRequest/UpdatePollRequest/UpstreamOptionDto.
• Each model carries custom (extraData) flattened to the JSON root via a CustomObjectDtoAdapter(extraDataPropertyName = "custom") registered in MoshiChatParser; votingVisibility uses the generated sealed class + its adapter.
• MoshiChatApi mappers and PollsApi @Body types retyped to the generated models.

Testing

• Serialization tests (CreatePollRequestAdapterTest, PollOptionInputAdapterTest, PollWriteRequestAdapterTest) lock the flattened wire shape for all 6 models; MoshiChatApiTest covers the mappers.
• spotlessApply, apiDump (no public-API change), detekt, and the full client testDebugUnitTest suite pass.
• Device probe against the real backend: createPoll/updatePoll/createPollOption/updatePollOption each send custom flattened at root and voting_visibility (both anonymous and public); all return 201 and echo the custom sentinel back.

[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	5.96 MB	5.95 MB	-0.02 MB	🚀
stream-chat-android-ui-components	11.22 MB	11.24 MB	0.02 MB	🟢
stream-chat-android-compose	12.71 MB	12.72 MB	0.00 MB	🟢

[sonarqubecloud]

Quality Gate failed

Failed conditions
63.1% Coverage on New Code (required ≥ 80%)
8.5% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud