[misc] Add conversions for unsigned types, torch > 2.3.0 (#8528)

### Brief Summary

pytorch 2.3.0 now has unsigned datatypes, add conversions for those from
taichi unsigned types.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bob Cao <bobcaocheng@gmail.com>

python/taichi/lang/util.py

@@ -166,9 +166,18 @@ def to_pytorch_type(dt):
         return torch.uint8
     if dt == f16:
         return torch.float16
+
     if dt in (u16, u32, u64):
-        raise RuntimeError(f"PyTorch doesn't support {dt.to_string()} data type.")
-    assert False
+        if hasattr(torch, "uint16"):
+            if dt == u16:
+                return torch.uint16
+            if dt == u32:
+                return torch.uint32
+            if dt == u64:
+                return torch.uint64
+        raise RuntimeError(f"PyTorch doesn't support {dt.to_string()} data type before version 2.3.0.")
+
+    raise RuntimeError(f"PyTorch doesn't support {dt.to_string()} data type.")
 
 
 def to_paddle_type(dt):
@@ -266,8 +275,16 @@ def to_taichi_type(dt):
             return u8
         if dt == torch.float16:
             return f16
-        if dt in (u16, u32, u64):
-            raise RuntimeError(f"PyTorch doesn't support {dt.to_string()} data type.")
+
+        if hasattr(torch, "uint16"):
+            if dt == torch.uint16:
+                return u16
+            if dt == torch.uint32:
+                return u32
+            if dt == torch.uint64:
+                return u64
+
+        raise RuntimeError(f"PyTorch doesn't support {dt.to_string()} data type before version 2.3.0.")
 
     if has_paddle():
         import paddle  # pylint: disable=C0415