So: I see in the manual that
> a[i:j:k] bit slicing by constant subscripts
is allowed. 
I want to bit slice based on "constants"— python constants, things which are either true constants stored in named variables or are values computed at "elaborate time"
So I say:
`self._led_attenuate_bits = range(0, attenuate_power)`
And then I say this, and it does not like it:
```
  File "/Users/mcc/work/f/template-fpga/src/counter.py", line 55, in elaborate
    self.may_light = self.current_led.count[self._led_attenuate_bits] == 0 \
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mcc/work/f/template-fpga/.venv/lib/pypy3.10/site-packages/amaranth/hdl/ast.py", line 287, in __getitem__
    raise TypeError("Cannot index value with {}".format(repr(key)))
TypeError: Cannot index value with range(0, 2)
```
Am I missing something?