Joke explanation generalization (#2899)

For the Issue #2827.
I have made changes to JokeExplaniation Class.
This PR implements the DatasetEntry class in the JokeExplaination class
to generalize the data. The DatasetEntry class provides a consistent
data structure for storing joke-explanation pairs, making it easier to
work with the data.
and made changes in AlpacaGpt4 to correct the annotation in one of its
methods.
The changes in this PR include:
- Adding a new DatasetEntry class to represent joke-explanation pairs
- Updating the JokeExplaination class to use DatasetEntry objects to
store data
- Replacing the AlpacaGpt4 class __getitem__ method with correct
annotation

---------

Co-authored-by: sampatkalyan <120446217+Andavarapu-Sampat-Kalyan@users.noreply.github.com>

model/model_training/custom_datasets/qa_datasets.py

@@ -333,8 +333,6 @@ def __init__(self, cache_dir) -> None:
             with open(joke_explain_filename, "w") as fout:
                 fout.write(content)
 
-        question = ""
-        answer = ""
         self.pairs = []
         with open(joke_explain_filename, "r") as f:
             for line in f:
@@ -343,16 +341,12 @@ def __init__(self, cache_dir) -> None:
                 # DO NOT change this
                 # its the data that had syntax error
                 explanation = data["explaination"]
-                self.pairs.append((joke, explanation))
+                self.pairs.append(DatasetEntry(questions=[joke], answers=[explanation]))
 
-        if len(question) > 0 and len(answer) > 0:
-            self.pairs.append((question, answer))
-        self.length = len(self.pairs)
-
-    def __len__(self):
+    def __len__(self) -> int:
         return self.length
 
-    def __getitem__(self, index):
+    def __getitem__(self, index) -> DatasetEntry:
         return self.pairs[index]
 
 
@@ -610,6 +604,6 @@ def _process_instruction(self, row: dict[str, str], input_max_length: int) -> Da
     def __len__(self) -> int:
         return len(self.rows)
 
-    def __getitem__(self, index: int) -> list[str] | tuple[str]:
+    def __getitem__(self, index: int) -> DatasetEntry:
         dialogue = self.rows[index]
         return dialogue