✨ Enable parenthesized lists in search criteria

[nevans]

This affects #search, #uid_search, #sort, #uid_sort, #thread, and #uid_thread#.

Prior to this, sending a parenthesized list in the search criteria for any of these commands required the use of strings, which are converted to RawData, which has security implications with untrusted inputs.

With this change, arrays will only be converted into SequenceSet when every element in the array is a valid SequenceSet input. Otherwise, the array will be left alone, which allows us to send parenthesized lists without using strings and RawData.

For example, some searches this change enables:

• combining criteria to pass into OR, NOT, FUZZY, etc.
  • search(["not", %w(flagged unread)]) converts to:
    SEARCH not (flagged unread)
• Adding return options (we should also add a return kwarg).
  • uid_search(["RETURN", ["PARTIAL", 1..50], "UID", 12345..67890] converts to:
    UID SEARCH RETURN (PARTIAL 1:50) UID 12345:67890
  • Note that PARTIAL supports negative ranges, which can't be coerced to SequenceSet.
    They'll need to be sent as strings, for now.
  • Note that searches with return options should return ESEARCH results, which are currently unsupported.
    See ✨ Add basic ESearch support #333.

This should be backward compatible: previously these inputs would simply raise an exception.