refactor(data_type): pin DataType enum values explicitly

The `AscendC` custom kernels forward `static_cast<int64_t>(input.dtype())`
to their `aclrtlaunch_*` entry points and dispatch on the same enum —
making `DataType`'s integer values part of a host↔device ABI.

Assign explicit values (`kInt8 = 0, …, kFloat64 = 11`) to pin that ABI:
reordering or inserting entries above existing ones would silently
change the integers seen by device code.  No behaviour change at call
sites (the enum is still accessed by symbolic name everywhere except
the `int64_t` cast).

Author: zhangyue

src/data_type.h

@@ -11,19 +11,26 @@
 
 namespace infini::ops {
 
+// Element-type tag shared across the project.  Values are assigned
+// explicitly because they are part of the ABI between the host-side
+// launcher wrappers (e.g. `src/ascend/rms_norm/kernel_custom.h`) and the
+// `aclrtlaunch_*` device kernels under `src/ascend/custom/**/op_kernel/`
+// — the launcher forwards `static_cast<int64_t>(input.dtype())` and the
+// kernel dispatches on it.  Reordering entries would silently break that
+// ABI.
 enum class DataType : std::int8_t {
-  kInt8,
-  kInt16,
-  kInt32,
-  kInt64,
-  kUInt8,
-  kUInt16,
-  kUInt32,
-  kUInt64,
-  kFloat16,
-  kBFloat16,
-  kFloat32,
-  kFloat64
+  kInt8 = 0,
+  kInt16 = 1,
+  kInt32 = 2,
+  kInt64 = 3,
+  kUInt8 = 4,
+  kUInt16 = 5,
+  kUInt32 = 6,
+  kUInt64 = 7,
+  kFloat16 = 8,
+  kBFloat16 = 9,
+  kFloat32 = 10,
+  kFloat64 = 11,
 };
 
 constexpr ConstexprMap<DataType, std::size_t, 12> kDataTypeToSize{{{