Fix: Avoid empty keyword argument in VLLMModelConfig from Makefile

[mattdepaolis]

Issue Summary
When running the make evaluate command with the specified parameters, an error occurs indicating that the VLLMModelConfig initializer received an unexpected keyword argument.

• Fixes : Error in make evaluate: TypeError: VLLMModelConfig.init() got an unexpected keyword argument '' #163

Steps to Reproduce:

1. Set up the environment as per the project's guidelines.
2. Execute the following command:

make evaluate MODEL=deepseek-ai/DeepSeek-R1-Distill-Qwen-1.5B TASK=math_500

3. Expected Behavior: The evaluation process should complete without errors, utilizing the specified model and task parameters.

4. Actual Behavior: The following error message is displayed:

TypeError: VLLMModelConfig.__init__() got an unexpected keyword argument ''

Root Cause Analysis

• The MODEL_ARGS variable in the Makefile's evaluate target includes an empty $(PARALLEL_ARGS), which introduces consecutive commas.
• This results in an empty string being passed as a keyword argument to VLLMModelConfig.

Proposed Solution
Modify the MODEL_ARGS assignment in the Makefile to conditionally include $(PARALLEL_ARGS) only if it's not empty:

MODEL_ARGS="pretrained=$(MODEL),dtype=bfloat16$(if $(PARALLEL_ARGS),,$(PARALLEL_ARGS)),max_model_length=32768,gpu_memory_utilisation=0.8"

This prevents the introduction of an unintended empty string argument.

Testing

• Ran the make evaluate command with and without PARALLEL_ARGS and verified that no unexpected keyword argument error occurs.

[Charlesnorris509]

@mattdepaolis This PR seems to be solid and follow best practices, however The evaluate target is quite complex and involves multiple nested conditionals and shell commands. This will be difficult to maintain.