Move xferinfo_cb to ollama_client.cpp to avoid exposing libcurl in header

- Remove curl/curl.h include from ollama_client.hpp
- Remove xferinfo_cb static method declaration from OllamaClient class
- Make xferinfo_cb a file-scope static function in ollama_client.cpp

Closes: #195

include/ollama_client.hpp

@@ -5,7 +5,6 @@
 #include <vector>
 #include <iostream>
 #include <optional>
-#include <curl/curl.h>
 
 using http_req_cb_t = std::function<std::string(std::string const& old, std::string const& new_str)>;
 
@@ -31,11 +30,6 @@ private:
     nlohmann::json build_body(const std::vector<Message>& messages,
                               const std::vector<Tool>& tools) const;
     static size_t write_cb(char* ptr, size_t size, size_t nmemb, void* userdata);
-    static int xferinfo_cb(void* cookie,
-                       curl_off_t dltotal,
-                       curl_off_t dlnow,
-                       curl_off_t ultotal,
-                       curl_off_t ulnow);
     std::expected<std::string, std::string> http_request(const std::string& full_url, 
                              const std::string& method, 
                              const std::string& body = "",

src/ollama_client.cpp

@@ -38,8 +38,7 @@ size_t OllamaClient::write_cb(char* ptr, size_t size, size_t nmemb, void* userda
     return size * nmemb;
 }
 
-
-int OllamaClient::xferinfo_cb(void* cookie,
+static int xferinfo_cb(void* cookie,
                        curl_off_t dltotal,
                        curl_off_t dlnow,
                        curl_off_t ultotal,