fix(BA-4879): Update vfolder client to match new REST API response format

[hhoikoo]

resolves #9662 (BA-4879)

Update the vfolder client SDK (client/func/vfolder.py) and CLI (client/cli/vfolder.py) to match the updated server REST API response format, and fix the resulting mypy type errors and unit test mocks.

The server now wraps single-item responses in {"item": {...}}. This PR unwraps that envelope in create(), info(), and clone() so callers receive the inner dict directly. Each unwrap site uses an explicit intermediate variable (item: dict[str, Any] = result["item"]) to satisfy mypy's no-any-return check. Additionally, _get_id_by_name() now sends the folder name as a query parameter (vfolder_name=) instead of a JSON body and reads the id from data["item"]["id"].

Field renames in CLI output are also applied to match the new API contract:

• numFiles -> num_files in vfolder info
• inviter_user_email -> inviter in vfolder invitations

Unit tests in tests/unit/client/test_vfolder.py and tests/unit/client/test_vfolder_tus.py are updated to reflect these changes: mock payloads are wrapped in {"item": ...}, and _get_id_by_name mocks use query-parameter URLs. The build_url helper in the TUS test module gains an optional params argument to support URL-encoded query parameters.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[Copilot]

Pull request overview

Updates the legacy vfolder client SDK and CLI output handling to align with the manager REST API’s updated response/field formats (notably the new single-item {"item": ...} envelope).

Changes:

• Unwrap {"item": ...} for vfolder create(), info(), clone(), and ID lookup (_get_id_by_name() reads data["item"]["id"]).
• Change vfolder ID lookup to pass the folder name via query param (vfolder_name=) instead of a JSON body.
• Update CLI output field names (numFiles → num_files, inviter_user_email → inviter).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
src/ai/backend/client/func/vfolder.py	Unwraps the new item envelope for several endpoints and updates ID lookup request/response parsing.
src/ai/backend/client/cli/vfolder.py	Adjusts displayed field names in vfolder info and vfolder invitations to match the new API contract.

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