feat: remote index stats (#1702)

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.

python/src/index.rs

@@ -200,6 +200,8 @@ pub struct IndexConfig {
     /// Currently this is always a list of size 1.  In the future there may
     /// be more columns to represent composite indices.
     pub columns: Vec<String>,
+    /// Name of the index.
+    pub name: String,
 }
 
 #[pymethods]
@@ -215,6 +217,7 @@ impl From<lancedb::index::IndexConfig> for IndexConfig {
         Self {
             index_type,
             columns: value.columns,
+            name: value.name,
         }
     }
 }