add start and end characters matching

Co-authored-by: Francesco Bruzzesi <[email protected]>

narwhals/_arrow/utils.py

@@ -341,8 +341,8 @@ def convert_str_slice_to_int_slice(
 DATE_RE = r"(?P<date>\d{1,4}[-/.]\d{1,2}[-/.]\d{1,4})"
 SEP_RE = r"(?P<sep>\s|T)"
 TIME_RE = r"(?P<time>\d{2}:\d{2}(?::\d{2})?)"  # \s*(?P<period>[AP]M)?)?
-HMS_RE = r"(?P<hms>\d{2}:\d{2}:\d{2})"
-HM_RE = r"(?P<hm>\d{2}:\d{2})"
+HMS_RE = r"^(?P<hms>\d{2}:\d{2}:\d{2})$"
+HM_RE = r"^(?P<hm>\d{2}:\d{2})$"
 TZ_RE = r"(?P<tz>Z|[+-]\d{2}:?\d{2})"  # Matches 'Z', '+02:00', '+0200', '+02', etc.
 FULL_RE = rf"{DATE_RE}{SEP_RE}?{TIME_RE}?{TZ_RE}?$"