feat(esp_partition): Add esp_partition_flash_binary() CMake function

Add a new CMake function esp_partition_flash_binary() that provides a
unified API for registering partition data binaries to be flashed. It
replaces the direct esptool_py_flash_target calls scattered across
components (spiffs, fatfs, nvs_flash) with a single function that:

- Resolves partition offset from the partition table automatically
- Determines encryption requirements (auto-detect or ALWAYS_PLAINTEXT)
- Creates per-partition flash targets (e.g. idf.py <partition>-flash)
- Optionally includes the binary in `idf.py flash` via FLASH_IN_PROJECT

On the linux target, the function registers binaries for pre-loading
into the emulated flash. A build-time manifest (linux_flash_data.txt)
is generated via file(GENERATE), and partition_linux.c reads it at
runtime to copy each binary into the memory-mapped flash buffer at
the correct offset.

The partition_ops example is updated to use the new function and
includes a custom_partition with pre-built data to demonstrate the
full workflow, including on the linux target.

components/spiffs/project_include.cmake

@@ -47,19 +47,15 @@ function(spiffs_create_partition_image partition base_dir)
             ADDITIONAL_CLEAN_FILES
             ${image_file})
 
-        idf_component_get_property(main_args esptool_py FLASH_ARGS)
-        idf_component_get_property(sub_args esptool_py FLASH_SUB_ARGS)
-        # Last (optional) parameter is the encryption for the target. In our
-        # case, spiffs is not encrypt so pass FALSE to the function.
-        esptool_py_flash_target(${partition}-flash "${main_args}" "${sub_args}" ALWAYS_PLAINTEXT)
-        esptool_py_flash_to_partition(${partition}-flash "${partition}" "${image_file}")
-
-        add_dependencies(${partition}-flash spiffs_${partition}_bin)
+        # Encryption for SPIFFS is not supported, so optional parameter ALWAYS_PLAINTEXT is passed to the function.
+        set(esp_partition_register_target_optional_args)
+        list(APPEND esp_partition_register_target_optional_args ALWAYS_PLAINTEXT DEPENDS spiffs_${partition}_bin)
 
         if(arg_FLASH_IN_PROJECT)
-            esptool_py_flash_to_partition(flash "${partition}" "${image_file}")
-            add_dependencies(flash spiffs_${partition}_bin)
+            list(APPEND esp_partition_register_target_optional_args FLASH_IN_PROJECT)
         endif()
+
+        esp_partition_register_target(${partition} "${image_file}" ${esp_partition_register_target_optional_args})
     else()
         set(message "Failed to create SPIFFS image for partition '${partition}'. "
                     "Check project configuration if using the correct partition table file.")