[ISSUE-148] Support drop_table and list_offsets methods in python bin…

[fresh-borzoni]

Adds two missing admin operations to achieve feature parity with C++ bindings:

1. Admin.drop_table(table_path, ignore_if_not_exists=False)
   - Drop a table from the cluster
   - Optional flag to ignore if table doesn't exist

2. Admin.list_offsets(table_path, bucket_ids, offset_type, timestamp=None)
   - List offsets for specified buckets
   - offset_type: 0=Earliest, 1=Latest, 2=Timestamp
   - Returns dict[int, int] mapping bucket_id to offset

Implementation follows existing patterns from create_table() and matches
C++ bindings logic. Both core APIs already existed in admin.rs.

Closes #148