Add comprehensive object_store test coverage (46 new tests)

New tests cover:
- get_info(): fields verification (name, bucket, size, chunks, nuid, deleted, digest, description, headers, metadata, modified, link)
- ObjectInfo.__str__() representation
- seal(): sealing bucket and verifying sealed state prevents puts
- list(): listing objects, empty bucket, iterator.next() with timeout
- watch(): basic watch, with_history, without_history, multiple events, delete events, timeout, timedelta timeout
- link_object() and link_bucket(): creating links and verifying ObjectLink fields
- update_metadata(): description, rename, headers, metadata
- put() with metadata, file path, custom chunk_size, all options combined, multi-value headers, empty data
- get() with custom chunk_size
- ObjectInfoIterator: __aiter__ protocol
- ObjectStoreConfig: all options, setters, defaults, full options creation
- Error handling: get/get_info nonexistent objects, get nonexistent bucket
- Multiple objects in a single bucket
- Delete then get_info (verify deleted=True)
- Overwrite preserves bucket info

Co-authored-by: s3rius <18153319+s3rius@users.noreply.github.com>
Agent-Logs-Url: https://github.com/taskiq-python/natsrpy/sessions/e3f8e778-1ed5-4c2d-8191-b7bd8cf10425

Author: Copilot