perf: cache get_compute_capability (#1456)

<!-- .github/pull_request_template.md -->

## 📌 Description

Cache compute capability to reduce repeat cpu overload mentioned in
#1425 (comment)

Results reproduced from
https://gist.github.com/yzh119/d9bf2abbb667abcbb806979f4bbea633 :
```bash
before the fix
w/o CUDAGraph 0.0054492950439453125
w/  CUDAGraph 0.002916574478149414
after the fix
w/o CUDAGraph 0.0038330554962158203
w/  CUDAGraph 0.0030286312103271484
```

## 🔍 Related Issues

#1425

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## 🧪 Tests

- [x] Tests have been added or updated as needed.
- [x] All tests are passing (`unittest`, etc.).

## Reviewer Notes

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Co-authored-by: Yaxing Cai <[email protected]>

Author: cyx-6

flashinfer/utils.py

@@ -14,6 +14,7 @@
 limitations under the License.
 """
 
+import functools
 import math
 import os
 from enum import Enum
@@ -207,6 +208,7 @@ def canonicalize_torch_dtype(dtype: Union[torch.dtype, str]) -> torch.dtype:
         )
 
 
+@functools.cache
 def get_compute_capability(device: torch.device) -> Tuple[int, int]:
     if device.type != "cuda":
         raise ValueError("device must be a cuda device")