chore: update Lance to v15.0.0-beta.2 (#4690)

**Blocked on the corrected Lance release:**
https://github.com/lance-format/lance/pull/10370 restores the `Send`
contract required by downstream Function workers. Refresh this upgrade
with that release before merging.

Upgrade the Rust, Java, and Python Lance dependencies to
https://github.com/lance-format/lance/releases/tag/v15.0.0-beta.2. This
brings in bounded vector-index consolidation without retraining
(https://github.com/lance-format/lance/pull/10335) and deletion
filtering for index entries whose fragment coverage was pruned
(https://github.com/lance-format/lance/pull/10325).

Synchronize the vendored `lance-arrow` with the release and retain its
offset-safe validity patch. The existing `nullable_struct_merge`
regression still panics with the unpatched release, so removing that
patch would regress nullable nested queries. Refresh both lockfiles,
including the `zstd-sys` version required by the new Lance encoding
dependency.

Update the custom memtable bitmap test adapter to train on row
addresses, matching the new bitmap contract; remove its obsolete row-ID
conversion.

Preserve the Blob APIs' existing missing-row error messages when newer
Lance rejects a missing fragment earlier in the read path. Retain
upstream attribution in vendored sources while satisfying the repository
license-header check.

Validation of the compatibility fixes: all 58 Rust Blob integration
tests and 219 Python Blob tests pass (one Python test skipped). Strict
workspace Clippy, formatting, and diff checks pass.

java/pom.xml

@@ -28,7 +28,7 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <arrow.version>15.0.0</arrow.version>
-        <lance-core.version>15.0.0-beta.1</lance-core.version>
+        <lance-core.version>15.0.0-beta.2</lance-core.version>
         <jackson.version>2.18.11</jackson.version>
         <spotless.skip>false</spotless.skip>
         <spotless.version>2.30.0</spotless.version>