Fix str_title_case skipping later lowercase-exception words after a leading occurrence

[patchwright]

Problem

In str_title_case, the lowercase-exception pass bails out of the whole
loop the first time a match is found at the start of the string:

for pos in findall(string_lower, exception):
    is_start = pos < 2
    if is_start:
        break        # aborts every remaining occurrence of this word

findall yields every position of the exception word. The intent of the
is_start guard is to leave the leading word capitalized — but break
abandons all later occurrences too, so a small word that appears once at the
start and again later never gets lowercased:

>>> from mnamer.utils import str_title_case
>>> str_title_case("the cat in the hat")
'The Cat in The Hat'      # expected: 'The Cat in the Hat'
>>> str_title_case("a man and a plan")
'A Man and A Plan'        # expected: 'A Man and a Plan'

Fix

Use continue instead of break, so only the leading occurrence is skipped
and later ones are still processed. One-word change.

Tests

Added test_str_title_case__lower__repeated_after_start covering a
lowercase-exception word that recurs after the start (the cat in the hat,
its uppercase variant, and a man and a plan). Verified it fails on the
previous code and passes with the fix. The full local suite (347 tests)
passes, and ruff check / ruff format --check are clean.