Fix missing low-level api imports (#856)

## Summary
Some of the imports specified in the Readme don't work, this is a small
fix to make them work.

<!---
## Details
This is an optional section; is there anything specific that reviewers
should be aware of?
--->

## Testing Done
<!--- This is a required section; please describe how this change was
tested. --->

<!-- 
Replace BLANK with your device type. For example, A100-80G-PCIe
A100

Complete the following tasks before sending your PR, and replace `[ ]`
with
`[x]` to indicate you have done them. 
-->

- Hardware Type: <BLANK>
- [x] run `make test` to ensure correctness
- [x] run `make checkstyle` to ensure code style
- [x] run `make test-convergence` to ensure convergence

Author: Kirill-Kravtsov

src/liger_kernel/transformers/__init__.py

@@ -10,11 +10,15 @@
 from liger_kernel.transformers.fused_linear_jsd import LigerFusedLinearJSD  # noqa: F401
 from liger_kernel.transformers.geglu import LigerGEGLUMLP  # noqa: F401
 from liger_kernel.transformers.jsd import LigerJSD  # noqa: F401
+from liger_kernel.transformers.kl_div import LigerKLDIVLoss  # noqa: F401
 from liger_kernel.transformers.layer_norm import LigerLayerNorm  # noqa: F401
 from liger_kernel.transformers.llama4_rope import liger_llama4_text_rotary_pos_emb  # noqa: F401
 from liger_kernel.transformers.llama4_rope import liger_llama4_vision_rotary_pos_emb  # noqa: F401
+from liger_kernel.transformers.multi_token_attention import LigerMultiTokenAttention  # noqa: F401
 from liger_kernel.transformers.rms_norm import LigerRMSNorm  # noqa: F401
 from liger_kernel.transformers.rope import liger_rotary_pos_emb  # noqa: F401
+from liger_kernel.transformers.softmax import LigerSoftmax  # noqa: F401
+from liger_kernel.transformers.sparsemax import LigerSparsemax  # noqa: F401
 from liger_kernel.transformers.swiglu import LigerBlockSparseTop2MLP  # noqa: F401
 from liger_kernel.transformers.swiglu import LigerPhi3SwiGLUMLP  # noqa: F401
 from liger_kernel.transformers.swiglu import LigerQwen3MoeSwiGLUMLP  # noqa: F401
@@ -134,6 +138,10 @@ def __getattr__(name: str):
     "LigerQwen3MoeSwiGLUMLP",
     "LigerSwiGLUMLP",
     "LigerTVDLoss",
+    "LigerKLDIVLoss",
+    "LigerMultiTokenAttention",
+    "LigerSoftmax",
+    "LigerSparsemax",
 ]
 
 # Add transformer-dependent symbols only if available

src/liger_kernel/transformers/experimental/__init__.py

@@ -0,0 +1,5 @@
+from liger_kernel.transformers.experimental.embedding import LigerEmbedding  # noqa: F401
+
+__all__ = [
+    "LigerEmbedding",
+]