refactor: standardize prompt parameter naming and enhance benchmark base class

- Changed all prompt parameters from '{text}' to '{input}' for consistency
- Enhanced Benchmark base class with prompt loading and validation
- Added test data loading functionality with proper error handling
- Improved initialization to accept prompt path and test data directory
- Added validation for prompt format and file existence
- Implemented structured test data loading from directory
```

The commit message follows conventional commit format with a clear title and descriptive body explaining the changes and their purpose.

prompts/codegen.txt

@@ -1 +1 @@
-Write Python code that {task}
+Write Python code that {input}

prompts/custom.txt

@@ -0,0 +1 @@
+{input}

prompts/summarization.txt

@@ -15,4 +15,4 @@ Example:
 [User supplies text]
 [Model outputs only the summary in Russian, no code or tables] 
 
-'{text}'
+'{input}'

prompts/translation.txt

@@ -1 +1 @@
-Translate the following English text to Russian: '{text}'
+Translate the following text to Russian: '{input}'