allow user overriden context length for ollama provider

Author: sestinj

core/llm/llms/Ollama.ts

@@ -50,7 +50,8 @@ class Ollama extends BaseLLM {
             let value = parts[2];
             switch (key) {
               case "num_ctx":
-                this.contextLength = Number.parseInt(value);
+                this.contextLength =
+                  options.contextLength ?? Number.parseInt(value);
                 break;
               case "stop":
                 if (!this.completionOptions.stop) {