libc: wcsftime is absent (PS5MC); fix branch ready #3625

libc (libSceLibcInternal) does not export wcsftime (NID XbVXpf5WF28). From the relink registry order it is a predicted stop of PS5MC (PPSA99420, index 481); not yet observed in a run.

Fix branch ready: screamm:feat/libc-wcsftime (06ed477e, one commit on main a11c8f7f). I cannot open it as a PR because of the intake check; anyone eligible is welcome to carry it, keeping the commit as is.

• wcsftime(buf, maxsize, format, tm) in Time.cpp follows FreeBSD 11.4 lib/libc/locale/wcsftime.c (8c639945) step by step over the repository's own wcsrtombs, strftime and mbsrtowcs with the 16-bit guest wchar_t in the C locale (none.c/table.c, the only locale setlocale accepts here): a format character above 255 returns 0 with EILSEQ, an unrepresentable maxsize * MB_CUR_MAX returns 0 with EINVAL, allocation failure ENOMEM; an empty result, a result that does not fit and a null buffer return 0 with errno unchanged and the buffer untouched; null format or tm throw (FreeBSD dereferences both). One host difference found and contained: the Windows CRT strftime sets ERANGE/EINVAL on overflow or zero size where FreeBSD's does not, so wcsftime restores errno around the call (the guest strftime export still leaks those values; left for a separate change). TechnicalDebt records the sources.
• guest_wide_formatting compares wcsftime with strftime unit by unit for a fixed tm over the common conversions, a Latin-1 round trip, pinned outputs, the zero-return cases with errno kept, EILSEQ, EINVAL and the throws.

Tested on Windows 11 Pro 26220, WinLibs MinGW-w64 GCC 15.2.0 r7, Ninja, Release, BUILD_TESTING=ON, full build including libs: guest_wide_formatting and guest_time_conversion 3/3; ctest -j8 -E "^agc_driver_|^video_out_flip" 533/536, the failures being the known windows_exceptions (#3411), guest_kernel_sys (#3510) and guest_filesystem (#3518); with main's Time.cpp the extended test fails; tools/check_conventions.py --base main and git diff --check pass. Not run on Linux.

Written with Claude Code assistance (implementation by a subagent, reviewed and validated in this session).