[Misc] Add __all__ in __init__.py. (#478)

This PR adds __all__ in __init__.py to constrain the imported objects.

Signed-off-by: Yuchuan <[email protected]>

Author: Seven-Streams

python/xgrammar/__init__.py

@@ -25,3 +25,32 @@
 )
 from .structural_tag import StructuralTag
 from .tokenizer_info import TokenizerInfo, VocabType
+
+__all__ = [
+    "exception",
+    "structural_tag",
+    "testing",
+    "CompiledGrammar",
+    "GrammarCompiler",
+    "get_max_recursion_depth",
+    "get_serialization_version",
+    "max_recursion_depth",
+    "set_max_recursion_depth",
+    "hf",
+    "DeserializeFormatError",
+    "DeserializeVersionError",
+    "InvalidJSONError",
+    "InvalidStructuralTagError",
+    "Grammar",
+    "StructuralTagItem",
+    "BatchGrammarMatcher",
+    "GrammarMatcher",
+    "allocate_token_bitmask",
+    "apply_token_bitmask_inplace",
+    "bitmask_dtype",
+    "get_bitmask_shape",
+    "reset_token_bitmask",
+    "StructuralTag",
+    "TokenizerInfo",
+    "VocabType",
+]