feat: speed up unmarshaller (#101)

src/dbus_fast/_private/unmarshaller.pxd

@@ -50,6 +50,10 @@ cdef class Unmarshaller:
 
     cpdef read_uint32_cast(self, object type_)
 
+    cpdef read_int16_cast(self, object type_)
+
+    cdef _read_int16_cast(self)
+
     cpdef read_string_unpack(self, object type_)
 
     cdef _read_string_unpack(self)

src/dbus_fast/_private/unmarshaller.py

@@ -245,6 +245,9 @@ class Unmarshaller:
         return self._view[self._pos - UINT32_SIZE : self._pos].cast(UINT32_CAST)[0]
 
     def read_int16_cast(self, type_: SignatureType) -> int:
+        return self._read_int16_cast()
+
+    def _read_int16_cast(self) -> int:
         self._pos += INT16_SIZE + (-self._pos & (INT16_SIZE - 1))  # align
         return self._view[self._pos - INT16_SIZE : self._pos].cast(INT16_CAST)[0]
 
@@ -291,10 +294,13 @@ class Unmarshaller:
         tree = get_signature_tree(self._read_signature())
         signature_type = tree.types[0]
         # verify in Variant is only useful on construction not unmarshalling
+        token = signature_type.token
+        if token == "n" and self._uint32_unpack is None:
+            return Variant(tree, self._read_int16_cast(), False)
         return Variant(
             tree,
-            self._readers[signature_type.token](self, signature_type),
-            verify=False,
+            self._readers[token](self, signature_type),
+            False,
         )
 
     def read_struct(self, type_: SignatureType) -> List[Any]:

src/dbus_fast/signature.py

@@ -443,5 +443,13 @@ class Variant:
 
 
 @lru_cache(maxsize=None)
-def get_signature_tree(signature: str = "") -> SignatureTree:
+def get_signature_tree(signature: str) -> SignatureTree:
+    """Get a signature tree for the given signature.
+
+    :param signature: The signature to get a tree for.
+    :type signature: str
+
+    :returns: The signature tree for the given signature.
+    :rtype: :class:`SignatureTree`
+    """
     return SignatureTree(signature)