Enhance printing functionality with SNMP support and update dependencies

- Added SNMP configuration options to `AppConfig` for querying printer status.
- Extended `PrintInstruction` in the proto file to support additional fields for remote file URLs and raw data.
- Implemented logic in `CupsClient` to retrieve printer paper levels and page counts via SNMP.
- Updated `Cargo.toml` to include `snmp` and `reqwest` dependencies for network communication.
- Refactored `TempPdf` handling to support multiple data sources for printing.
- Improved error handling and logging for better diagnostics during print operations.

proto/control.proto

@@ -39,8 +39,12 @@ message Pong {
 
 message PrintInstruction {
   string request_id = 1;
-  bytes pdf_data = 2;
+  bytes pdf_data = 2;      // 兼容旧字段，仍可用
   PrintParams params = 3;
+  string url = 4;          // 新：远程文件 URL
+  bytes raw_data = 5;      // 新：任意二进制（预期 PDF）
+  string local_path = 6;   // 新：本地路径（客户端可读）
+  string content_type = 7; // 可选 MIME 类型，默认 application/pdf
 }
 
 message PrintParams {
@@ -78,5 +82,7 @@ message PrinterInfo {
   uint32 ppm = 9;
   uint32 ppm_color = 10;
   repeated string reasons = 11;
+  int32 paper_percent = 12; // -1 或缺省表示未知
+  uint64 page_count = 13;   // 总页数，0 或缺省表示未知
 }