feat: add a basic async python client starting point (#1014)

This changes `lancedb` from a "pure python" setuptools project to a
maturin project and adds a rust lancedb dependency.

The async python client is extremely minimal (only `connect` and
`Connection.table_names` are supported). The purpose of this PR is to
get the infrastructure in place for building out the rest of the async
client.

Although this is not technically a breaking change (no APIs are
changing) it is still a considerable change in the way the wheels are
built because they now include the native shared library.

python/python/tests/test_remote_db.py

@@ -0,0 +1,41 @@
+#  Copyright 2023 LanceDB Developers
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+import lancedb
+import pyarrow as pa
+from lancedb.remote.client import VectorQuery, VectorQueryResult
+
+
+class FakeLanceDBClient:
+    def close(self):
+        pass
+
+    def query(self, table_name: str, query: VectorQuery) -> VectorQueryResult:
+        assert table_name == "test"
+        t = pa.schema([]).empty_table()
+        return VectorQueryResult(t)
+
+    def post(self, path: str):
+        pass
+
+    def mount_retry_adapter_for_table(self, table_name: str):
+        pass
+
+
+def test_remote_db():
+    conn = lancedb.connect("db://client-will-be-injected", api_key="fake")
+    setattr(conn, "_client", FakeLanceDBClient())
+
+    table = conn["test"]
+    table.schema = pa.schema([pa.field("vector", pa.list_(pa.float32(), 2))])
+    table.search([1.0, 2.0]).to_pandas()