Implement missing str_to_polarstype case for String (#204)

* Implement missing `str_to_polarstype` case for String

* test that pl.String works in “df from rows with schema”

Author: controversial

__tests__/dataframe.test.ts

@@ -2449,10 +2449,10 @@ describe("additional", () => {
     expect(dfs).toEqual(expected);
   });
   test("df from rows with schema", () => {
-    const rows = [{ a: 1, b: 2, c: null }];
+    const rows = [{ a: 1, b: 2, c: null, d: "foo" }];
 
     const df = pl.DataFrame(rows, {
-      schema: { a: pl.Int32, b: pl.Int32, c: pl.Utf8 },
+      schema: { a: pl.Int32, b: pl.Int32, c: pl.Utf8, d: pl.String },
       orient: "row",
     });
     const actual = df.toRecords();

src/conversion.rs

@@ -657,6 +657,7 @@ impl FromNapiValue for Wrap<DataType> {
                     "Float64" => DataType::Float64,
                     "Bool" => DataType::Boolean,
                     "Utf8" => DataType::String,
+                    "String" => DataType::String,
                     "List" => {
                         let inner = obj.get::<_, Array>("inner")?.unwrap();
                         let inner_dtype: Object = inner.get::<Object>(0)?.unwrap();