feat: added alternative solution and TLE solution to decode-ways problem, wrote the tutorial file and added some more manual test cases

decode-ways/problem.json

@@ -43,9 +43,9 @@
     },
     "solutions": {
         "main-ac": "ac.cpp",
-        "alternative-ac": [],
+        "alternative-ac": ["alternative_ac.cpp"],
         "wrong-answer": [],
-        "time-limit": [],
+        "time-limit": ["TLE.cpp"],
         "time-limit-or-ac": [],
         "time-limit-or-memory-limit": [],
         "memory-limit": [],