feat: add EskinDeviceFunc FFI bindings and update Python/README

- Add FFI wrappers for all EskinDeviceFunc trait methods:
  eskin_read_hdw_version, eskin_read_matrix_row/col,
  eskin_read_device_config1/2, eskin_write_device_config1/2,
  eskin_write_matrix_row/col
- Extract sdk_error_to_code() helper for SdkError -> SdkErrorCode conversion
- Update C header (include/eskin_ffi.h) with new function declarations
- Update Python FFI bindings (example/python/eskin_ffi.py) with new methods
- Update README with Python usage instructions and full FFI interface table

include/eskin_ffi.h

@@ -60,6 +60,59 @@ EskinSdkErrorCode eskin_write_register(
     uint16_t* return_count
 );
 
+// Device function interfaces (EskinDeviceFunc)
+
+EskinSdkErrorCode eskin_read_hdw_version(
+    EskinDeviceHandle handle,
+    char* buf,
+    uint32_t buf_len,
+    uint32_t* actual_len
+);
+
+EskinSdkErrorCode eskin_read_matrix_row(
+    EskinDeviceHandle handle,
+    uint8_t* out
+);
+
+EskinSdkErrorCode eskin_read_matrix_col(
+    EskinDeviceHandle handle,
+    uint8_t* out
+);
+
+EskinSdkErrorCode eskin_read_device_config1(
+    EskinDeviceHandle handle,
+    uint8_t* out
+);
+
+EskinSdkErrorCode eskin_read_device_config2(
+    EskinDeviceHandle handle,
+    uint8_t* out
+);
+
+EskinSdkErrorCode eskin_write_device_config1(
+    EskinDeviceHandle handle,
+    bool enable,
+    uint16_t* return_count
+);
+
+EskinSdkErrorCode eskin_write_device_config2(
+    EskinDeviceHandle handle,
+    bool enable,
+    uint16_t* return_count
+);
+
+EskinSdkErrorCode eskin_write_matrix_row(
+    EskinDeviceHandle handle,
+    uint8_t row,
+    uint16_t* return_count
+);
+
+EskinSdkErrorCode eskin_write_matrix_col(
+    EskinDeviceHandle handle,
+    uint8_t col,
+    uint16_t* return_count
+);
+
 #ifdef __cplusplus
 }
 #endif