feat(namespace-dir): implement rename_table for DirectoryNamespace

Summary

Implement rename_table for DirectoryNamespace to allow renaming tables within the same namespace at the directory level.

Motivation

The LanceNamespace trait defines a rename_table method, but DirectoryNamespace currently falls back to the default "not implemented" behavior. This blocks use cases where tables need to be renamed in directory-based namespace deployments (e.g., COS / GooseFS connectors).

Requirements

Core Functionality

• Validate input: reject empty new_table_name
• Verify source table exists via resolve_table_location
• Check destination table does not already exist (conflict detection)
• Copy all files from source table directory to destination path
• Remove source directory after successful copy
• Update manifest entries when manifest mode is enabled (drop old + register new)

Cross-Namespace Rename

• Reject cross-namespace rename when manifest mode is disabled (return Unsupported error)
• Delegate cross-namespace rename to ManifestNamespace when manifest mode is enabled

Error Handling

• Return InvalidInput for empty table name
• Return TableNotFound when source table does not exist
• Return TableAlreadyExists when destination table already exists
• Return Unsupported for cross-namespace rename without manifest
• Return Internal for filesystem operation failures

Acceptance Criteria

• rename_table works correctly in both manifest-enabled and manifest-disabled modes
• All files (manifests, data fragments, indices, etc.) are correctly moved
• Original table is no longer accessible after rename
• Renamed table is fully accessible (describe, query, etc.)
• Unit tests cover: basic rename, conflict detection, source not found, empty name validation, cross-namespace rejection

Related

• Part of the namespace operations roadmap (PR-C in the PR breakdown plan)
• Depends on: resolve_table_location, table_exists, remove_dir_all

Start at DirectoryNamespace's LanceNamespace implementation and trace resolve_table_location, table_exists, and remove_dir_all. Compare ManifestNamespace handling for cross-namespace operations, then add coverage for same-namespace moves, conflicts, missing sources, empty names, and manifest-disabled rejection; done means the destination is accessible and the source is gone.