feat(python): support large_utf8 function signatures (#4092)

Teach the Python Function signature emitter to serialize PyArrow large
strings as the canonical Arrow type name `large_utf8`.

Extend the shared Function Arrow type fixture and explicit-schema
coverage for scalar, nested, list, and large-list compositions.

rust/lancedb/tests/fixtures/first_class_functions/v1/arrow_types.json

@@ -78,6 +78,12 @@
         "type": "utf8"
       }
     },
+    {
+      "arrow_type": "large_utf8",
+      "json": {
+        "type": "large_utf8"
+      }
+    },
     {
       "arrow_type": "binary",
       "json": {
@@ -171,6 +177,21 @@
         ]
       }
     },
+    {
+      "arrow_type": "list<large_utf8>",
+      "json": {
+        "type": "list",
+        "fields": [
+          {
+            "name": "item",
+            "nullable": false,
+            "type": {
+              "type": "large_utf8"
+            }
+          }
+        ]
+      }
+    },
     {
       "arrow_type": "large_list<utf8>",
       "json": {
@@ -186,6 +207,21 @@
         ]
       }
     },
+    {
+      "arrow_type": "large_list<large_utf8>",
+      "json": {
+        "type": "large_list",
+        "fields": [
+          {
+            "name": "item",
+            "nullable": false,
+            "type": {
+              "type": "large_utf8"
+            }
+          }
+        ]
+      }
+    },
     {
       "arrow_type": "fixed_size_list<float32, 384>",
       "json": {
@@ -330,4 +366,4 @@
     "timestamp[us]",
     "struct<a: int32>"
   ]
-}
+}