FuriHalRtc refactor: new datetime lib (#3386)

* datetimelib created
* datetimelib unit tests added
* firmware fixes to new datetimelib
* typo fix
* merge artifacts fixed, datetimelib renamed to datetime

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

lib/datetime/datetime.h

@@ -0,0 +1,75 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+    // Time
+    uint8_t hour; /**< Hour in 24H format: 0-23 */
+    uint8_t minute; /**< Minute: 0-59 */
+    uint8_t second; /**< Second: 0-59 */
+    // Date
+    uint8_t day; /**< Current day: 1-31 */
+    uint8_t month; /**< Current month: 1-12 */
+    uint16_t year; /**< Current year: 2000-2099 */
+    uint8_t weekday; /**< Current weekday: 1-7 */
+} DateTime;
+
+/** Validate Date Time
+ *
+ * @param      datetime  The datetime to validate
+ *
+ * @return     { description_of_the_return_value }
+ */
+bool datetime_validate_datetime(DateTime* datetime);
+
+/** Convert DateTime to UNIX timestamp
+ * 
+ * @warning    Mind timezone when perform conversion
+ *
+ * @param      datetime  The datetime (UTC)
+ *
+ * @return     UNIX Timestamp in seconds from UNIX epoch start
+ */
+uint32_t datetime_datetime_to_timestamp(DateTime* datetime);
+
+/** Convert UNIX timestamp to DateTime
+ *
+ * @warning    Mind timezone when perform conversion
+ *
+ * @param[in]  timestamp  UNIX Timestamp in seconds from UNIX epoch start
+ * @param[out] datetime   The datetime (UTC)
+ */
+void datetime_timestamp_to_datetime(uint32_t timestamp, DateTime* datetime);
+
+/** Gets the number of days in the year according to the Gregorian calendar.
+ *
+ * @param year Input year.
+ *
+ * @return number of days in `year`.
+ */
+uint16_t datetime_get_days_per_year(uint16_t year);
+
+/** Check if a year a leap year in the Gregorian calendar.
+ *
+ * @param year Input year.
+ *
+ * @return true if `year` is a leap year.
+ */
+bool datetime_is_leap_year(uint16_t year);
+
+/** Get the number of days in the month.
+ *
+ * @param leap_year true to calculate based on leap years
+ * @param month month to check, where 1 = January
+ * @return the number of days in the month
+ */
+uint8_t datetime_get_days_per_month(bool leap_year, uint8_t month);
+
+#ifdef __cplusplus
+}
+#endif