[ENH] Update error message printed on overlapping cycles to be more verbose

[jwlodek]

The error message will now print out which keys were duplicated. Addresses bluesky/bluesky#1768

Example output:

...
...
  File "/home/jwlodek/Workspace/cycler/cycler/__init__.py", line 288, in __add__
    return Cycler(
           ^^^^^^^
  File "/home/jwlodek/Workspace/cycler/cycler/__init__.py", line 181, in __init__
    self._keys: set[K] = _process_keys(self._left, self._right)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jwlodek/Workspace/cycler/cycler/__init__.py", line 85, in _process_keys
    raise ValueError(f"Cannot compose overlapping cycles, duplicate key(s): {l_key & r_key}")
ValueError: Cannot compose overlapping cycles, duplicate key(s): {SoftPositioner(name='my_positioner1', settle_time=0.0, timeout=None, egu='', limits=(0, 0), source='computed')}

[timhoffm]

Thanks @jwlodek!