Use newer sgkit/zarr calling conventions

This removes a couple of deprecation warnings

tests/test_variantdata.py

@@ -80,14 +80,14 @@ def test_sgkit_dataset_roundtrip(tmp_path):
     inf_ts = tsinfer.infer(samples)
     ds = sgkit.load_dataset(zarr_path)
 
-    assert ts.num_individuals == inf_ts.num_individuals == ds.dims["samples"]
+    assert ts.num_individuals == inf_ts.num_individuals == ds.sizes["samples"]
     for ts_ind, sample_id in zip(inf_ts.individuals(), ds["sample_id"].values):
         assert ts_ind.metadata["variant_data_sample_id"] == sample_id
 
     assert (
-        ts.num_samples == inf_ts.num_samples == ds.dims["samples"] * ds.dims["ploidy"]
+        ts.num_samples == inf_ts.num_samples == ds.sizes["samples"] * ds.sizes["ploidy"]
     )
-    assert ts.num_sites == inf_ts.num_sites == ds.dims["variants"]
+    assert ts.num_sites == inf_ts.num_sites == ds.sizes["variants"]
     assert ts.sequence_length == inf_ts.sequence_length == ds.attrs["contig_lengths"][0]
     for (
         v,
@@ -122,7 +122,7 @@ def test_sgkit_individual_metadata_not_clobbered(tmp_path):
     inf_ts = tsinfer.infer(samples)
     ds = sgkit.load_dataset(zarr_path)
 
-    assert ts.num_individuals == inf_ts.num_individuals == ds.dims["samples"]
+    assert ts.num_individuals == inf_ts.num_individuals == ds.sizes["samples"]
     for i, (ts_ind, sample_id) in enumerate(
         zip(inf_ts.individuals(), ds["sample_id"].values)
     ):
@@ -694,23 +694,15 @@ def test_phased(self, tmp_path):
             ds["call_genotype"].dims,
             np.ones(ds["call_genotype"].shape, dtype=bool),
         )
-        ds["variant_ancestral_allele"] = (
-            ds["variant_position"].dims,
-            np.array(["A", "C", "G"], dtype="S1"),
-        )
         sgkit.save_dataset(ds, path)
-        tsinfer.VariantData(path, "variant_ancestral_allele")
+        tsinfer.VariantData(path, ds["variant_allele"][:, 0].values.astype(str))
 
     def test_ploidy1_missing_phase(self, tmp_path):
         path = tmp_path / "data.zarr"
         # Ploidy==1 is always ok
         ds = sgkit.simulate_genotype_call_dataset(n_variant=3, n_sample=3, n_ploidy=1)
-        ds["variant_ancestral_allele"] = (
-            ds["variant_position"].dims,
-            np.array(["A", "C", "G"], dtype="S1"),
-        )
         sgkit.save_dataset(ds, path)
-        tsinfer.VariantData(path, "variant_ancestral_allele")
+        tsinfer.VariantData(path, ds["variant_allele"][:, 0].values.astype(str))
 
     def test_ploidy1_unphased(self, tmp_path):
         path = tmp_path / "data.zarr"
@@ -719,12 +711,8 @@ def test_ploidy1_unphased(self, tmp_path):
             ds["call_genotype"].dims,
             np.zeros(ds["call_genotype"].shape, dtype=bool),
         )
-        ds["variant_ancestral_allele"] = (
-            ds["variant_position"].dims,
-            np.array(["A", "C", "G"], dtype="S1"),
-        )
         sgkit.save_dataset(ds, path)
-        tsinfer.VariantData(path, "variant_ancestral_allele")
+        tsinfer.VariantData(path, ds["variant_allele"][:, 0].values.astype(str))
 
     def test_duplicate_positions(self, tmp_path):
         path = tmp_path / "data.zarr"
@@ -749,14 +737,10 @@ def test_empty_alleles_not_at_end(self, tmp_path):
             ds["variant_allele"].dims,
             np.array([["", "A", "C"], ["A", "C", ""], ["A", "C", ""]], dtype="S1"),
         )
-        ds["variant_ancestral_allele"] = (
-            ["variants"],
-            np.array(["C", "A", "A"], dtype="S1"),
-        )
         sgkit.save_dataset(ds, path)
-        samples = tsinfer.VariantData(path, "variant_ancestral_allele")
+        vdata = tsinfer.VariantData(path, ds["variant_allele"][:, 0].values.astype(str))
         with pytest.raises(ValueError, match="Empty alleles must be at the end"):
-            tsinfer.infer(samples)
+            tsinfer.infer(vdata)
 
     def test_unimplemented_from_tree_sequence(self):
         # NB we should reimplement something like this functionality.