Improve handling of ArrayFlags

Why discord did it this way instead of as an integer bitfield like everything
reasonable is unknowable, but this does less work to get to the same result.

Add comment detailing what many would find unreadbale

discord/flags.py

@@ -25,6 +25,7 @@ DEALINGS IN THE SOFTWARE.
 from __future__ import annotations
 
 from functools import reduce
+from operator import or_
 from typing import TYPE_CHECKING, Any, Callable, ClassVar, Dict, Iterator, List, Optional, Tuple, Type, TypeVar, overload
 
 from .enums import UserFlags
@@ -1566,7 +1567,15 @@ class ArrayFlags(BaseFlags):
     @classmethod
     def _from_value(cls: Type[Self], value: List[int]) -> Self:
         self = cls.__new__(cls)
-        self.value = reduce(lambda a, b: a | (1 << b - 1), value, 0)
+        # This is a micro-optimization given the frequency this object can be created.
+        # (1).__lshift__ is used in place of lambda x: 1 << x
+        # prebinding to a method of a constant rather than define a lambda.
+        # Pairing this with map, is essentially equivalent to (1 << x for x in value)
+        # reduction using operator.or_ instead of defining a lambda each call
+        # Discord sends these starting with a value of 1
+        # Rather than subtract 1 from each element prior to left shift,
+        # we shift right by 1 once at the end.
+        self.value = reduce(or_, map((1).__lshift__, value), 0) >> 1
         return self
 
     def to_array(self) -> List[int]: