Generalize QS8 VADD[C] templates to cover QU8 VADD[C] microkernels

- QU8 VADD[C] SSE2 MUL16 microkernels
- QU8 VADD[C] NEON microkernels
- QU8 VADD[C] WAsm SIMD microkernels
- QU8 VADD[C] scalar microkernels
- Unit tests

PiperOrigin-RevId: 385931044
diff --git a/src/qs8-vaddc/avx2-mul32-ld64.c.in b/src/qs8-vaddc/avx2-mul32-ld64.c.in
index 736a619..0992813 100644
--- a/src/qs8-vaddc/avx2-mul32-ld64.c.in
+++ b/src/qs8-vaddc/avx2-mul32-ld64.c.in
@@ -3,6 +3,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
+$assert DATATYPE in ["QS8", "QU8"]
 $assert BATCH_TILE % 8 == 0
 $assert BATCH_TILE >= 8
 $ABC = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"