feat!: change default read_consistency_interval=5s (#2281)

Previously, when we loaded the next version of the table, we would block
all reads with a write lock. Now, we only do that if
`read_consistency_interval=0`. Otherwise, we load the next version
asynchronously in the background. This should mean that
`read_consistency_interval > 0` won't have a meaningful impact on
latency.

Along with this change, I felt it was safe to change the default
consistency interval to 5 seconds. The current default is `None`, which
means we will **never** check for a new version by default. I think that
default is contrary to most users expectations.

python/python/tests/test_db.py

@@ -3,7 +3,6 @@
 
 
 import re
-from datetime import timedelta
 import os
 
 import lancedb
@@ -299,13 +298,11 @@ def test_create_exist_ok(tmp_db: lancedb.DBConnection):
 @pytest.mark.asyncio
 async def test_connect(tmp_path):
     db = await lancedb.connect_async(tmp_path)
-    assert str(db) == f"ListingDatabase(uri={tmp_path}, read_consistency_interval=None)"
-
-    db = await lancedb.connect_async(
-        tmp_path, read_consistency_interval=timedelta(seconds=5)
-    )
     assert str(db) == f"ListingDatabase(uri={tmp_path}, read_consistency_interval=5s)"
 
+    db = await lancedb.connect_async(tmp_path, read_consistency_interval=None)
+    assert str(db) == f"ListingDatabase(uri={tmp_path}, read_consistency_interval=None)"
+
 
 @pytest.mark.asyncio
 async def test_close(mem_db_async: lancedb.AsyncConnection):
@@ -453,7 +450,7 @@ async def test_open_table(tmp_path):
     assert tbl.name == "test"
     assert (
         re.search(
-            r"NativeTable\(test, uri=.*test\.lance, read_consistency_interval=None\)",
+            r"NativeTable\(test, uri=.*test\.lance, read_consistency_interval=5s\)",
             str(tbl),
         )
         is not None