refactor(index): introduce lance-index-core crate with abstract index trait layer

Extracts the abstract trait layer for scalar indices into a new
`lance-index-core` crate (~17 deps vs 75+ in lance-index), enabling
index plugin authors to implement ScalarIndex without depending on
the full lance-index implementation crate.

Moved to lance-index-core: Index, IndexType, IndexParams, MetricsCollector,
ScalarIndex, AnyQuery, IndexStore/Reader/Writer, RowIdRemapper, SearchResult,
CreatedIndex, UpdateCriteria, OldIndexDataFilter, ScalarIndexParams,
BuiltinIndexType, TrainingCriteria/TrainingOrdering, IndexFile.

lance-index and lance-table re-export all moved types for backward
compatibility. FragReuseIndex/MemWalIndex trait impls move to lance-table
where those types are defined.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

refactor(index): break lance-table → lance-index-core dependency

Remove the unintended `lance-table → lance-index-core` dependency introduced
in the previous commit. Key changes:

- Restore `IndexFile` as a standalone struct in `lance-table` (duplicate of
  the one in `lance-index-core`), removing the re-export that forced the dep
- Add `index_files_to_table()` / `table_files_to_index()` free functions in
  `lance-index` to convert between the two distinct `IndexFile` types
- Introduce newtype wrappers `FragReuseIndexHandle` and `MemWalIndexHandle` in
  `lance-index` so that `Index` / `RowIdRemapper` (now in `lance-index-core`)
  can be implemented on the `lance-table` types without violating orphan rules
- Remove the `lance-index-core` trait impls that were added directly on
  `FragReuseIndex` / `MemWalIndex` in `lance-table`
- Update all call sites in `lance`, `lance-index`, and `lance-namespace-impls`
  to use the handle newtypes and conversion functions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: westonpace

.bumpversion.toml

@@ -80,6 +80,11 @@ filename = "Cargo.toml"
 search = 'lance-index = {{ version = "={current_version}"'
 replace = 'lance-index = {{ version = "={new_version}"'
 
+[[tool.bumpversion.files]]
+filename = "Cargo.toml"
+search = 'lance-index-core = {{ version = "={current_version}"'
+replace = 'lance-index-core = {{ version = "={new_version}"'
+
 [[tool.bumpversion.files]]
 filename = "Cargo.toml"
 search = 'lance-io = {{ version = "={current_version}"'

Cargo.lock

@@ -9,6 +9,7 @@ members = [
     "rust/lance-file",
     "rust/lance-geo",
     "rust/lance-index",
+    "rust/lance-index-core",
     "rust/lance-io",
     "rust/lance-linalg",
     "rust/lance-namespace",
@@ -67,6 +68,7 @@ lance-encoding = { version = "=9.0.0-beta.21", path = "./rust/lance-encoding" }
 lance-file = { version = "=9.0.0-beta.21", path = "./rust/lance-file" }
 lance-geo = { version = "=9.0.0-beta.21", path = "./rust/lance-geo" }
 lance-index = { version = "=9.0.0-beta.21", path = "./rust/lance-index" }
+lance-index-core = { version = "=9.0.0-beta.21", path = "./rust/lance-index-core" }
 lance-io = { version = "=9.0.0-beta.21", path = "./rust/lance-io", default-features = false }
 lance-linalg = { version = "=9.0.0-beta.21", path = "./rust/lance-linalg" }
 lance-namespace = { version = "=9.0.0-beta.21", path = "./rust/lance-namespace" }

Cargo.toml

@@ -255,7 +255,7 @@ impl Hnsw {
         rt().block_on(Some(py), async {
             let batch = self.hnsw.to_batch()?;
             let metadata = batch.schema_ref().metadata().clone();
-            writer.write_record_batch(batch).await?;
+            writer.write(&[batch]).await?;
             writer.finish_with_metadata(&metadata).await?;
             Result::Ok(())
         })?

java/lance-jni/Cargo.lock

@@ -0,0 +1,33 @@
+[package]
+name = "lance-index-core"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+license.workspace = true
+repository.workspace = true
+readme = "README.md"
+description = "Core traits and types for Lance index plugins"
+keywords.workspace = true
+categories.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+async-trait.workspace = true
+arrow-array.workspace = true
+arrow-schema.workspace = true
+arrow-select.workspace = true
+bytes.workspace = true
+datafusion-common.workspace = true
+datafusion-expr.workspace = true
+datafusion.workspace = true
+futures.workspace = true
+lance-core.workspace = true
+lance-io.workspace = true
+lance-select.workspace = true
+prost-types.workspace = true
+roaring.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+
+[lints]
+workspace = true