feat: bring the MemWAL LSM surface to parity across the SDKs

Four of the eight LSM methods are remote-only in the core: `impl BaseTable
for NativeTable` implements only set/unset/get_lsm_write_spec and
close_lsm_writers, while flush_lsm, compact_lsm and get_lsm_stats fall
through to trait defaults returning NotSupported. That is why Node had
bound the four that work locally and stopped, and why the remaining four
had no binding-level coverage anywhere.

Node: add napi bindings for flush_lsm, compact_lsm, checkpoint_lsm and
get_lsm_stats, with typed LsmStats/BucketStats/GenerationStats/
MemtableStats objects mirroring the existing LsmWriteSpec object in the
same file. Tests assert each binding reaches the core and surfaces
NotSupported locally; behavior against a real endpoint stays covered by
the mocked-endpoint tests in rust/lancedb/src/remote/table.rs.

Python: LsmWriteSpec was importable only from the private lancedb._lancedb
-- it appeared in table.py solely under `if TYPE_CHECKING:`. Export it as
lancedb.LsmWriteSpec, add it to __all__, and list it in the API reference,
which had no mention of it and so rendered it nowhere.

Java: add the LSM routes to lancedb-core. Java reaches LanceDB purely over
REST through the generated namespace client, and these routes are not in
the Lance Namespace spec, so they are issued through a small dedicated
client. LsmWriteSpec is deliberately not org.lance.memwal.
InitializeMemWalParams: that type defaults to maintaining no indexes where
a spec here defaults to maintaining every index, and it cannot express the
null that asks the server to resolve the set. checkpointLsm is ported from
rust/lancedb/src/table/checkpoint.rs with its constants and status
semantics intact -- 429/503 retried in place, 421 restarting from flush.

Note: `mvnw spotless:apply` cannot run on JDK 21 (google-java-format 1.7,
pinned in java/pom.xml, predates JDK 16's compiler API change). This is
pre-existing and reproduces on a pristine main checkout; the Java sources
here were formatted by hand to the checkstyle rules.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

python/python/lancedb/__init__.py

@@ -12,6 +12,7 @@ __version__ = importlib.metadata.version("lancedb")
 
 from ._lancedb import connect as lancedb_connect
 from ._lancedb import FtsToken
+from ._lancedb import LsmWriteSpec
 from ._lancedb import tokenize as _tokenize
 from .common import URI, sanitize_uri
 from urllib.parse import urlparse
@@ -518,6 +519,7 @@ __all__ = [
     "Job",
     "LanceDBConnection",
     "LanceNamespaceDBConnection",
+    "LsmWriteSpec",
     "RemoteDBConnection",
     "Session",
     "Table",

python/python/lancedb/table.py

@@ -4801,7 +4801,7 @@ class AsyncTable:
 
         Examples
         --------
-        >>> from lancedb._lancedb import LsmWriteSpec
+        >>> from lancedb import LsmWriteSpec
         >>> # table.set_unenforced_primary_key("id")
         >>> # table.set_lsm_write_spec(LsmWriteSpec.bucket("id", 16))
         """