Improve question generation efficiency In Response Relevancy metrics (#1810)

**Description**: This update refactors the _ascore method to use
asyncio.gather for parallel execution of question generation tasks. Key
improvements include:

**Issue** : When ResponseRelevancy evaluation loops based on the
strictness variable (default 3), which is taking longer than expected

**Performance Enhancement**: By processing all tasks concurrently, the
overall execution time is significantly reduced, especially for high
strictness values.
**Code Simplification**: The refactored code is more concise and aligns
better with Python's asynchronous programming patterns.
**Scalability**: The new implementation handles a larger number of tasks
without blocking, making it more suitable for use cases requiring high
concurrency.
**Backward Compatibility**: All existing functionality remains intact,
with no changes required to external interfaces.

This change improves the efficiency and maintainability of the codebase,
aligning with best practices for asynchronous programming in Python.

Result after resolution : Average 1 run of Example code based on
tutorial code (10 runs total) reduced to 4.35s => 2.82s

Author: hundredeuk2

src/ragas/metrics/_answer_relevance.py

@@ -16,6 +16,7 @@
     SingleTurnMetric,
 )
 from ragas.prompt import PydanticPrompt
+import asyncio
 
 logger = logging.getLogger(__name__)
 
@@ -136,14 +137,15 @@ async def _ascore(self, row: t.Dict, callbacks: Callbacks) -> float:
         assert self.llm is not None, "LLM is not set"
 
         prompt_input = ResponseRelevanceInput(response=row["response"])
-        responses = []
-        for _ in range(self.strictness):
-            response = await self.question_generation.generate(
+        tasks = [
+            self.question_generation.generate(
                 data=prompt_input,
                 llm=self.llm,
                 callbacks=callbacks,
             )
-            responses.append(response)
+            for _ in range(self.strictness)
+        ]
+        responses = await asyncio.gather(*tasks)
 
         return self._calculate_score(responses, row)