fix(core): enable thinking explicitly in flash-lite models (#3033)

Co-authored-by: Lee James <40045512+leehagoodjames@users.noreply.github.com>

packages/core/src/core/client.ts

@@ -243,6 +243,7 @@ export class GeminiClient {
         ? {
             ...this.generateContentConfig,
             thinkingConfig: {
+              thinkingBudget: -1,
               includeThoughts: true,
             },
           }