Migrate channel update and member request bodies to the generated UpdateChannelRequest model

[gpunto]

Goal

Migrate the channel update and member request bodies to the generated UpdateChannelRequest model.

Part of AND-1291

Implementation

• Replace six hand-written request bodies with the single generated UpdateChannelRequest:
  AcceptInviteRequest, RejectInviteRequest, AddMembersRequest, RemoveMembersRequest,
  InviteMembersRequest and the old UpdateChannelRequest. The endpoint takes one shape, so the
  separate wrappers collapse into it.
• Add the generated MessageRequest, ChannelInputRequest, ChannelMemberRequest, Attachment,
  Action, Field, Images, ImageData, SharedLocation, ConfigOverridesRequest and UserResponse.
• Add Message.toMessageRequest() for the system message these endpoints can carry, plus
  MessageRequestAdapter, AttachmentRequestAdapter, ChannelMemberRequestAdapter and
  ChannelInputRequestAdapter so custom data is flattened to the root on the way out.

Testing

• UpdateChannelRequestAdapterTest covers the serialized body for each of the collapsed calls, including
  the flattened custom data.
• Device-probed the member and invite endpoints on the wire.

[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	6.00 MB	0.03 MB	🟢
stream-chat-android-ui-components	11.26 MB	11.29 MB	0.03 MB	🟢
stream-chat-android-compose	12.74 MB	12.78 MB	0.04 MB	🟢

[gpunto]

Parking this until the OpenAPI spec generator is fixed.

monolith/openapi/spec/spec.go maps Go float64 to format: float in SchemaFormatFromReflectType, so SharedLocation.latitude/longitude are generated as 32-bit Float even though the backend stores float64. This branch would narrow those coordinates and lose sub-meter GPS precision compared to the hand-written DTO it replaces. Patching the vendored model is not an option, since the next regeneration would revert it.

Reopening once the spec emits format: double, at which point the regenerated model is Double and no workaround is needed.

[sonarqubecloud]

Quality Gate failed

Failed conditions
43.2% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[gpunto]

Superseded by #6634 (this PR cannot be reopened after the branch was force-pushed).