[JIT kernel] Update jit_kernel cache and develop doc (#17842)

python/sglang/jit_kernel/add_constant.py

@@ -1,17 +1,16 @@
 from __future__ import annotations
 
-import functools
 from typing import TYPE_CHECKING
 
 import torch
 
-from sglang.jit_kernel.utils import load_jit, make_cpp_args
+from sglang.jit_kernel.utils import cache_once, load_jit, make_cpp_args
 
 if TYPE_CHECKING:
     from tvm_ffi.module import Module
 
 
-@functools.cache
+@cache_once
 def _jit_add_constant_module(constant: int) -> Module:
     args = make_cpp_args(constant)  # pass all the template argument
     return load_jit(