fix: Bits.__getitem__/__setitem__ ignore msb_last (rtl) as documented

list() always used MSB-first bit order regardless of the msb_last
constructor flag, so indexing/slicing on an instance built with
msb_last=True silently behaved identically to the default -- the
documented "swap bit order for indexing and slicing" never happened.
__setitem__ needed a matching fix: since __setvalue() always expects
a MSB-first list, a mutated LSB-first list from list() has to be
reversed back before being passed in.

Found while wiring bits.Bits into progpib's GPIB status-byte handling
(IEEE-488.2 bit numbering is LSB-first, e.g. RQS = bit 6).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/bits.py

@@ -605,6 +605,9 @@ class Bits:
         l = self.list()
         # str->int->bool->int : accept bool, str, int, return either "0" or "1"
         l[index] = Bit(value)
+        if self.__r_to_l:
+            # list() returned LSB-first order; __setvalue expects MSB-first
+            l = l[::-1]
         self.__setvalue(l)
 
     def __get__(self, instance, owner):
@@ -911,10 +914,15 @@ class Bits:
         """
         self.__r_to_l = bool(msb_last)
 
-    def list(self, pad=True, reverse=False):
+    def list(self, pad=True, reverse=None):
         """
         Return self as list(of Bit)
+        reverse: True/False to force bit order for this call; None (the
+                 default) uses self.rtl, so indexing/slicing on an instance
+                 constructed with msb_last=True is LSB-first as documented.
         """
+        if reverse is None:
+            reverse = self.__r_to_l
         ret = []
         bits = self.bin(pad=pad, reverse=reverse)
         for b in bits: