misc: return type overload for return_lse (#578)

Make mypy and pylance happy.

For example, here's screenshots of vscode viewing
`test_batch_decode_kernels.py`.

return_lse=False:

![return_lse=False](https://github.com/user-attachments/assets/625919ca-04f8-4f37-b4b0-d89c15423c51)

return_lse=True:

![return_lse=True](https://github.com/user-attachments/assets/53a01a2b-c8b2-4629-922e-ca8dc8fad18c)

python/flashinfer/decode.py

@@ -17,7 +17,7 @@
 import functools
 import math
 from types import SimpleNamespace
-from typing import Any, List, Optional, Tuple, Union
+from typing import Any, List, Literal, Optional, Tuple, Union, overload
 
 import torch
 
@@ -831,6 +831,28 @@ def forward(
             q, paged_kv_cache, q_scale=q_scale, k_scale=k_scale, v_scale=v_scale
         )
 
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        paged_kv_cache: Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]],
+        q_scale: Optional[float] = None,
+        k_scale: Optional[float] = None,
+        v_scale: Optional[float] = None,
+        return_lse: Literal[False] = False,
+    ) -> torch.Tensor: ...
+
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        paged_kv_cache: Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]],
+        q_scale: Optional[float] = None,
+        k_scale: Optional[float] = None,
+        v_scale: Optional[float] = None,
+        return_lse: Literal[True] = True,
+    ) -> Tuple[torch.Tensor, torch.Tensor]: ...
+
     def run(
         self,
         q: torch.Tensor,

python/flashinfer/prefill.py

@@ -18,7 +18,7 @@
 import logging
 import math
 from types import SimpleNamespace
-from typing import Any, List, Optional, Tuple, Union
+from typing import Any, List, Literal, Optional, Tuple, Union, overload
 
 import torch
 
@@ -371,6 +371,46 @@ def single_prefill_with_kv_cache_with_jit_module(
     return (out, lse) if return_lse else out
 
 
+@overload
+def single_prefill_with_kv_cache(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    v: torch.Tensor,
+    custom_mask: Optional[torch.Tensor] = None,
+    packed_custom_mask: Optional[torch.Tensor] = None,
+    causal: bool = False,
+    kv_layout: str = "NHD",
+    pos_encoding_mode: str = "NONE",
+    allow_fp16_qk_reduction: bool = False,
+    sm_scale: Optional[float] = None,
+    window_left: int = -1,
+    logits_soft_cap: Optional[float] = None,
+    rope_scale: Optional[float] = None,
+    rope_theta: Optional[float] = None,
+    return_lse: Literal[False] = False,
+) -> torch.Tensor: ...
+
+
+@overload
+def single_prefill_with_kv_cache(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    v: torch.Tensor,
+    custom_mask: Optional[torch.Tensor] = None,
+    packed_custom_mask: Optional[torch.Tensor] = None,
+    causal: bool = False,
+    kv_layout: str = "NHD",
+    pos_encoding_mode: str = "NONE",
+    allow_fp16_qk_reduction: bool = False,
+    sm_scale: Optional[float] = None,
+    window_left: int = -1,
+    logits_soft_cap: Optional[float] = None,
+    rope_scale: Optional[float] = None,
+    rope_theta: Optional[float] = None,
+    return_lse: Literal[True] = True,
+) -> Tuple[torch.Tensor, torch.Tensor]: ...
+
+
 def single_prefill_with_kv_cache(
     q: torch.Tensor,
     k: torch.Tensor,
@@ -1077,6 +1117,26 @@ def forward(
         self._rope_theta = rope_theta
         return self.run(q, paged_kv_cache, k_scale=k_scale, v_scale=v_scale)
 
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        paged_kv_cache: Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]],
+        k_scale: Optional[float] = None,
+        v_scale: Optional[float] = None,
+        return_lse: Literal[False] = False,
+    ) -> torch.Tensor: ...
+
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        paged_kv_cache: Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]],
+        k_scale: Optional[float] = None,
+        v_scale: Optional[float] = None,
+        return_lse: Literal[True] = True,
+    ) -> Tuple[torch.Tensor, torch.Tensor]: ...
+
     def run(
         self,
         q: torch.Tensor,
@@ -1643,6 +1703,24 @@ def forward(
         self._rope_theta = rope_theta
         return self.run(q, k, v)
 
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        k: torch.Tensor,
+        v: torch.Tensor,
+        return_lse: Literal[False] = False,
+    ) -> torch.Tensor: ...
+
+    @overload
+    def run(
+        self,
+        q: torch.Tensor,
+        k: torch.Tensor,
+        v: torch.Tensor,
+        return_lse: Literal[True] = True,
+    ) -> Tuple[torch.Tensor, torch.Tensor]: ...
+
     def run(
         self,
         q: torch.Tensor,