feat: add BaseLanceNamespace that provides an implementation of all APIs through the Lance Rust SDK

[wombatu-kun]

Closes #171

Add lance-namespace-base crate — a filesystem/object-store-backed implementation of the LanceNamespace trait that delegates all operations directly to the Lance Rust SDK (Dataset, Scanner, index APIs, etc.).

Implementation

• Hierarchical namespaces mapped to directories with .lance-namespace marker files
• Tables stored as {namespace_path}/{table_name}.lance datasets
• Full trait coverage: all 47 LanceNamespace methods implemented, including namespace CRUD, table CRUD, data operations (insert/merge-insert/update/delete/query), index management (scalar, vector, FTS), versioning (list/create/describe/batch-delete/restore), schema alterations, tags, transactions, and query plan explain/analyze
• Builder pattern with support for storage options, Lance sessions, and from_properties() construction
• Pagination support for list operations (tables, indices, tags)
• register_table and alter_transaction return Unsupported as they are not applicable to a direct filesystem namespace

[github-actions]

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