[Core] Refactor AssertionEngine to address issues from description

[priyanshus]

What happened?

Issues

• Dead Code: Unused searchPaths Variable Line No - 98
• Probably this will cause an issue but before fixing make sure we test it throughly.
  const sdkPromptsDirSource = path.resolve(__dirname, '../../prompts');
  const sdkPromptsDirDist = path.resolve(__dirname, './prompts');
• Centralize Prompt Discovery: Move the logic for resolving prompt file paths into a dedicated service or into PromptLoader. The AssertionEngine should not be concerned with file system path resolution.
• Update unit tests.

Context around prompts

• Evaliphy consumers can provide their own prompts through evaliphy.config.ts file. There is a key promptsDir which should be respected if set by user.
• If prompts are not available under promptsDir , the SDK should fallback to prompts shipped by it.

Reproduction steps

No response

Evaliphy version

No response

Relevant log output

[silkiy]

Hi @priyanshus , this looks like a great 'good first issue' for me to tackle. I'd love to work on this! Could you please assign it to me? I plan to centralize the path resolution logic into a new PromptLoader service and ensure the unit tests cover the user config and fallback scenarios as described.