TupleManager string inputs: cryptic ValueError for bare strings, silent key/value shredding for 2-char elements

[derek73]

TupleManager (and RegexTupleManager) inherit dict.__init__ unchanged, so string inputs behave inconsistently with the guarded SetManager (#238):

from nameparser.config import Constants, TupleManager

Constants(capitalization_exceptions='ab')
# ValueError: dictionary update sequence element #0 has length 1; 2 is required
# loud, but names no argument and suggests no fix

TupleManager(['ab', 'cd'])                   # {'a': 'b', 'c': 'd'} — silent
Constants(capitalization_exceptions=['ii'])  # {'i': 'i'} — silent

The bare-string case fails loudly but cryptically (dict internals, ValueError where the sibling set-backed args now raise a friendly TypeError). The worse case is the silent one: an iterable of 2-character strings is a valid dict-update sequence, so each string shreds into a key/value pair with no error — same family as #238 through the mapping constructor.

Fix: give TupleManager an __init__ that rejects str/bytes outright (mirroring SetManager._reject_bare_string's message style) and rejects non-tuple string elements, closing the 2-char variant.

Found by review of PR #240 — pre-existing, unrelated to that change.