♻️ refactor OpenAI client options and unify custom headers parsing

Use OpenAI.ClientOptions for stronger typing and clarity
Extract custom headers parsing into parseCustomHeaders util
Simplify getEngine by delegating header parsing to helper
Improve maintainability and reduce code duplication

src/engine/openAi.ts

@@ -14,21 +14,17 @@ export class OpenAiEngine implements AiEngine {
   constructor(config: OpenAiConfig) {
     this.config = config;
 
-    // Configuration options for the OpenAI client
-    const clientOptions: any = {
+    const clientOptions: OpenAI.ClientOptions = {
       apiKey: config.apiKey
     };
     
-    // Add baseURL if present
     if (config.baseURL) {
       clientOptions.baseURL = config.baseURL;
     }
     
-    // Add custom headers if present
     if (config.customHeaders) {
       try {
         let headers = config.customHeaders;
-        // If the headers are a string, try to parse them as JSON
         if (typeof config.customHeaders === 'string') {
           headers = JSON.parse(config.customHeaders);
         }
@@ -37,7 +33,6 @@ export class OpenAiEngine implements AiEngine {
           clientOptions.defaultHeaders = headers;
         }
       } catch (error) {
-        // Silently ignore parsing errors
       }
     }