fix: reject empty column alterations and unknown Python keys (#4417)

Fixes #4390

Lance accepts column alterations with every change field unset, so a
path-only Python call could commit a new local version without changing
the schema. The Python binding also silently discarded unknown keys such
as `nulable`.

Validate every alteration in the shared Rust `Table` API before
dispatching to either backend, and reject unknown dictionary keys in the
Python binding while preserving the legacy `name` alias. Invalid batches
leave local schema and version unchanged and send no remote request.

Validation:

- Reproduced both reported calls on the original extension: versions
advanced from 1 to 2 to 3 with an unchanged schema; all 13 new
invalid-input Python cases failed before the fix.
- Rebuilt the extension with `uv run --extra tests --extra dev maturin
develop --extras tests,dev`; all 18 focused Python cases pass across
sync/async and local/mocked remote tables.
- `cargo test --quiet --features remote -p lancedb --lib alter_column`:
all eight tests pass, including both new regressions.
- `cargo clippy --quiet --features remote --tests --examples` passes
across the workspace.
- `cargo fmt --all`, `ruff check .`, and `ruff format .` pass.
- `typos` 1.26.0 passes across the repository; intentional misspellings
in regression fixtures use the existing line-specific spelling
exemptions.

<!-- lance-gatekeeper-fix:v1 agent=36a547cd11108898893456042e38628b
generation=1 -->

---------

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>

python/python/tests/test_remote_db.py

@@ -119,6 +119,77 @@ async def test_async_remote_db():
         assert table_names == []
 
 
+@pytest.mark.parametrize(
+    "alteration, match",
+    [
+        ({"path": "id"}, "One of rename, nullable or data_type"),
+        (
+            {"path": "id", "nulable": False},  # spellchecker:disable-line
+            "Unknown column alteration key 'nulable'",  # spellchecker:disable-line
+        ),
+        (
+            {
+                "path": "id",
+                "rename": "new_id",
+                "nulable": False,  # spellchecker:disable-line
+            },
+            "Unknown column alteration key 'nulable'",  # spellchecker:disable-line
+        ),
+    ],
+)
+def test_remote_alter_columns_rejects_invalid_before_request(alteration, match):
+    requests = []
+
+    def handler(request):
+        requests.append(request.path)
+        request.send_response(200)
+        request.send_header("Content-Type", "application/json")
+        request.end_headers()
+        request.wfile.write(b'{"version": 1, "schema": {"fields": []}}')
+
+    with mock_lancedb_connection(handler) as db:
+        table = db.open_table("test")
+        requests.clear()
+
+        with pytest.raises(ValueError, match=match):
+            table.alter_columns(alteration)
+
+        assert requests == []
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "alteration, match",
+    [
+        ({"path": "id"}, "One of rename, nullable or data_type"),
+        (
+            {"path": "id", "nulable": False},  # spellchecker:disable-line
+            "Unknown column alteration key 'nulable'",  # spellchecker:disable-line
+        ),
+    ],
+)
+async def test_async_remote_alter_columns_rejects_invalid_before_request(
+    alteration, match
+):
+    requests = []
+
+    def handler(request):
+        requests.append(request.path)
+        request.send_response(200)
+        request.send_header("Content-Type", "application/json")
+        request.end_headers()
+        request.wfile.write(b'{"version": 1, "schema": {"fields": []}}')
+
+    async with mock_lancedb_connection_async(handler) as db:
+        table = await db.open_table("test")
+        requests.clear()
+
+        with pytest.raises(ValueError, match=match):
+            await table.alter_columns(alteration)
+
+        assert requests == []
+
+
 @pytest.mark.asyncio
 async def test_async_checkout():
     def handler(request):