Feature Request: Add metadata parameter to volume creation (similar to sandbox create)

Is your feature request related to a problem? Please describe.

We need to associate custom metadata (e.g. underlying storage backend info, region, cluster, disk type, project/owner tags) with volumes at creation time. Currently Volume.create() only accepts a name parameter — there is no way to attach arbitrary key-value pairs to a volume. This makes it difficult to tag and organize volumes in multi-tenant environments and prevents storing operational metadata alongside the volume resource itself.

Describe the solution you'd like

Add a metadata: Optional[Dict[str, str]] parameter to volume creation, following the exact same pattern already used for sandboxes. This includes:

1. OpenAPI spec — Add VolumeMetadata schema (additionalProperties: {type: string}), and add metadata fields to NewVolume, Volume, ListedVolume schemas and the GET /volumes query parameters (for filtering).
2. API client model — Add metadata: Union[Unset, Dict[str, str]] to NewVolume in api/client/models/new_volume.py.
3. Python SDK — Add metadata: Optional[Dict[str, str]] to both Volume.create() and AsyncVolume.create(), pass it through to the API model, and surface it in VolumeAndToken/VolumeInfo types so it's available after creation.
4. Equivalent changes to JS SDK and CLI for consistency.

Example usage:

volume = Volume.create(
    name="my-data",
    metadata={
        "region": "us-east-1",
        "storage_class": "ssd",
        "project": "my-project",
    }
)

info = volume.get_info(volume.volume_id)
print(info.metadata)  # {"region": "us-east-1", ...}

Describe alternatives you've considered

• Encoding metadata in the volume name — fragile, limited, and not searchable via the API.
• Maintaining a separate metadata mapping service — adds unnecessary operational complexity for a feature that should be natively supported.

Additional context

Sandbox creation already supports this exact pattern end-to-end:

• Sandbox.create() accepts metadata: Optional[Dict[str, str]] (sandbox_sync/main.py:160)
• NewSandbox API model carries a metadata field (api/client/models/new_sandbox.py)
• SandboxMetadata is defined in the OpenAPI spec as additionalProperties: {type: string} (spec/openapi.yml:258-261)
• SandboxInfo.metadata surfaces it after creation (sandbox/sandbox_api.py:483)
• SandboxQuery.metadata supports filtering sandboxes by metadata when listing (sandbox/sandbox_api.py:565)

This request mirrors that same pattern for volumes.