pd.to_datetime should_cache errors with deque
```python
from collections import deque
pd.to_datetime(deque([Timestamp('2010-06-02 09:30:00')] * 51))
```

core.tools.datetimes.should_cache gives `sequence index must be integer, not 'slice` at  `unique(arg[:check_count])`

if deque is not expected it would make more sense to give a better message, otherwise support?

looks like a "good first issue" ?


version 0.25+ (i think it works on 0.24 but i only tested 0.25)