BREAKING CHANGE: the return value of `index_stats` method has changed
and all `index_stats` APIs now take index name instead of UUID. Also
several deprecated index statistics methods were removed.
* Removes deprecated methods for individual index statistics
* Aligns public `IndexStatistics` struct with API response from LanceDB
Cloud.
* Implements `index_stats` for remote Rust SDK and Python async API.
Before this we ignored the `fts_columns` parameter, and for now we
support to search on only one column, it could lead to an error if we
have multiple indexed columns for FTS
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Signed-off-by: BubbleCal <bubble-cal@outlook.com>
