Updated dependencies

• Google.Apis / Google.Apis.Auth / Google.Apis.Core → 1.76.0
• Google.Apis.Storage.v1 → 1.76.0.4250
• Google.Api.Gax / Google.Api.Gax.Rest → 4.15.0

Fixes:

• Object_Upload: Metadata is now optional. Added helpful description text to clarify usage.

New Features

• Custom metadata on upload: Object_Upload accepts an optional list of key-value pairs (e.g. user id, tenant, document type) stored with the object; Object_GetMetadata returns them in the new CustomMetadata output.
• Object_UpdateMetadata: change ContentType, ContentEncoding, ContentDisposition, CacheControl, and custom metadata without re-uploading the file. Only provided fields change; an entry with an empty Value removes that key. Concurrent updates are detected and fail cleanly instead of overwriting each other.
• Object_DeleteByPrefix: delete a "folder" (every object under a prefix) in a single server-side action, returning the number of objects deleted. The prefix is mandatory as a safety guard against wiping a whole bucket.