fix: str2time maps 4-digit pre-1970 years to future (RT#84075/GH#12)

t/gh12.t

@@ -0,0 +1,27 @@
+use strict;
+use warnings;
+use Test::More tests => 3;
+use Date::Parse qw(strptime str2time);
+
+# GH#12 / RT#84075: Date::Parse::str2time maps date in 1963 to 2063
+# Root cause: str2time passed a 2-digit year to timegm, triggering its 50-year
+# sliding window.  The fix: strptime extracts the century and returns year as
+# offset-from-1900; str2time reconstructs the full 4-digit year before calling
+# timegm, bypassing the windowing entirely.
+{
+    my $this_year = 1900 + (gmtime(time))[5];
+    my $target_year = $this_year - 50;
+    my $date = "$target_year-01-01 00:00:00 UTC";
+    my $time = str2time($date);
+    my $year_parsed_as = 1900 + (gmtime($time))[5];
+    is($year_parsed_as, $target_year, "GH#12: year $target_year not mapped to future");
+
+    # Canonical example from the original bug report (year 1963)
+    my $t1963 = str2time("1963-12-31 23:59:59 UTC");
+    my $got1963 = 1900 + (gmtime($t1963))[5];
+    is($got1963, 1963, "GH#12: 1963-12-31 not mapped to 2063");
+
+    # strptime must capture the century for 4-digit years
+    my @t = strptime("1963-12-31 23:59:59 UTC");
+    is($t[7], 19, "GH#12: strptime century field is 19 for 1963");
+}