feat(rtc): implement libSceRtc date and tick functions
- Ticks count microseconds since 0001-01-01 00:00:00 in the proleptic Gregorian calendar, up to 9999-12-31 23:59:59.999999. `sceRtcGetTickResolution` returns 1000000.
- Validation (`sceRtcCheckValid`, `sceRtcIsLeapYear`, `sceRtcGetDayOfWeek`) returns the matching `SCE_RTC_ERROR_INVALID_*` code (`0x80B50002`–`0x80B5000E`).
- Conversions: `sceRtcGetTick`/`SetTick`, `GetTime_t`/`SetTime_t`, `GetWin32FileTime`/`SetWin32FileTime`.
- Current time: `sceRtcGetCurrentTick`, `GetCurrentClock`, `GetCurrentClockLocalTime`. `sceRtcGetCurrentNetworkTick` uses the host clock.
- UTC and local time conversion through the host time zone.
- `sceRtcFormatRFC3339` (`YYYY-MM-DDThh:mm:ss.cc` plus `Z` or `±hh:mm`) and `sceRtcParseRFC3339`.
- Tick arithmetic (`sceRtcTickAdd*`) rejects results outside the valid range with `SCE_RTC_ERROR_INVALID_VALUE`.
- New exports: `sceRtcGetDaysInMonth`, `sceRtcTickAddMonths` and `sceRtcTickAddYears`. The last two clamp the day to the end of the target month (2024-01-31 + 1 month = 2024-02-29).