Migrate file upload and message translation to generated models

[gpunto]

Goal

Migrate the file upload response and the message translation request body to the generated network models.

Part of AND-1291

Implementation

• Add generated FileUploadResponse; remove the hand-written UploadFileResponse and rename its mapper and
  test to match. It covers all four upload endpoints (/channels/{type}/{id}/file,
  /channels/{type}/{id}/image, /uploads/file, /uploads/image).
• The generated file is nullable, matching the wire: Go tags it omitempty, so an empty asset URL is
  omitted and the old non-null file: String would have failed to parse. A response without a URL has
  nothing to attach, so toUploadedFile() now returns a Result and reports it as a failure;
  StreamFileUploader uses flatMap to carry that through.
• Add generated TranslateMessageRequest; remove the hand-written one. ChatClient.translate still takes
  a String, converted with Language.fromString, which falls back to Unknown and sends the value
  through unchanged, so an unsupported language is still rejected by the server rather than locally.
• Exclude the generated network/** path from the LongMethod detekt rule: the models map each wire enum
  in one exhaustive when (57 entries for Language), which a formatter cannot split and which would be
  regenerated anyway.

Testing

• UploadFileResponseMappingTest covers the mapping, a missing thumbnail, and the missing-URL failure.
• TranslateMessageRequestAdapterTest asserts the serialized body for a known language, for one the models
  do not know, and for every one of the 57 languages the endpoint accepts. Removing the Language adapter
  registration makes them fail.
• Device-probed all four upload endpoints plus translate. Every upload resolved a CDN URL, and all four
  returned no thumb_url, so the nullable thumbnail path is the normal shape rather than an edge case.
  translate sent {"language":"fr"}, unchanged from the hand-written body, and an invalid language was
  rejected by the server with its list of accepted values. That list matches the generated enum exactly,
  all 57 values.

[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	5.97 MB	0.01 MB	🟢
stream-chat-android-ui-components	11.26 MB	11.26 MB	0.00 MB	🟢
stream-chat-android-compose	12.74 MB	12.75 MB	0.01 MB	🟢

[sonarqubecloud]

Quality Gate failed

Failed conditions
79.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud