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/SConscript

@@ -0,0 +1,22 @@
+Import("env")
+
+env.Append(
+    LINT_SOURCES=[
+        Dir("."),
+    ],
+    CPPPATH=[
+        "#/lib/datetime",
+    ],
+    SDK_HEADERS=[
+        File("datetime.h"),
+    ],
+)
+
+libenv = env.Clone(FW_LIB_NAME="datetime")
+libenv.ApplyLibFlags()
+
+sources = libenv.GlobRecursive("*.c*")
+
+lib = libenv.StaticLibrary("${FW_LIB_NAME}", sources)
+libenv.Install("${LIB_DIST_DIR}", lib)
+Return("lib")