BUG: random seed is reset in PromptSampler resulting in nondeterministic runs

Basically the title. 

See: https://github.com/codelion/openevolve/blob/main/openevolve/prompt/sampler.py#L29
This will reset any random seed set by the user, and more importantly, set it to system time, which is effectively just random. 

<img width="2027" height="589" alt="Image" src="https://github.com/user-attachments/assets/44d5be0b-25ae-41c5-8af1-26e73a99fcb1" />