Speed up Punica compilation (#2632)

csrc/punica/bgmv/generator.py

+DTYPES = ["fp16", "bf16", "fp32"]
+DTYPE_MAP = {
+    "fp16": "nv_half",
+    "bf16": "nv_bfloat16",
+    "fp32": "float",
+}
+
+TEMPLATE = """
+#include "bgmv_config.h"
+#include "bgmv_impl.cuh"
+
+FOR_BGMV_WIDE_NARROW(INST_BGMV_TWOSIDE, {input_dtype}, {output_dtype}, {weight_dtype})
+""".lstrip()
+
+for input_dtype in DTYPES:
+    for output_dtype in DTYPES:
+        for weight_dtype in DTYPES:
+            if weight_dtype == "fp32":
+                # FP32 weights are not supported.
+                continue
+            kernel_definition = TEMPLATE.format(
+                input_dtype=DTYPE_MAP[input_dtype],
+                output_dtype=DTYPE_MAP[output_dtype],
+                weight_dtype=DTYPE_MAP[weight_dtype])
+            filename = f"bgmv_{input_dtype}_{output_dtype}_{weight_dtype}.cu"
+            with open(filename, "w") as f:
+                f.write(kernel_definition)