feat(usb): 引入统一的USB状态事件系统

重构USB事件管理，将原有的多个专用事件（usb_device_state_event、
usb_function_ready_event、usb_prepare_event）合并为统一的
usb_state_event。新的事件系统采用位标志方式管理USB状态，
提供更灵活的状态跟踪机制。

BREAKING CHANGE: 移除了旧的USB相关事件类型，需要更新依赖这些
事件的模块代码。

src/events/usb_state_event.c

@@ -0,0 +1,54 @@
+#include <caf/events/module_state_event.h>
+
+#include "usb_state_event.h"
+
+static const char *usb_state_event_op_name(uint8_t op)
+{
+	switch ((enum usb_state_event_op)op) {
+	case USB_STATE_EVENT_OP_SET_BITS:
+		return "set_bits";
+	case USB_STATE_EVENT_OP_CLEAR_BITS:
+		return "clear_bits";
+	case USB_STATE_EVENT_OP_SNAPSHOT:
+		return "snapshot";
+	default:
+		return "?";
+	}
+}
+
+static const char *module_name_or_any(const void *module_id)
+{
+	return (module_id != NULL) ? module_name_get(module_id) : "*";
+}
+
+static void log_usb_state_event(const struct app_event_header *aeh)
+{
+	const struct usb_state_event *event = cast_usb_state_event(aeh);
+
+	APP_EVENT_MANAGER_LOG(aeh,
+			      "src:%s sink:%s op:%s flags:0x%08x",
+			      module_name_or_any(event->src_module_id),
+			      module_name_or_any(event->sink_module_id),
+			      usb_state_event_op_name(event->op),
+			      event->flags);
+}
+
+static void profile_usb_state_event(struct log_event_buf *buf,
+				    const struct app_event_header *aeh)
+{
+	const struct usb_state_event *event = cast_usb_state_event(aeh);
+
+	nrf_profiler_log_encode_uint8(buf, event->op);
+	nrf_profiler_log_encode_uint32(buf, event->flags);
+}
+
+APP_EVENT_INFO_DEFINE(usb_state_event,
+		      ENCODE(NRF_PROFILER_ARG_U8, NRF_PROFILER_ARG_U32),
+		      ENCODE("op", "flags"),
+		      profile_usb_state_event);
+
+APP_EVENT_TYPE_DEFINE(usb_state_event,
+		      log_usb_state_event,
+		      &usb_state_event_info,
+		      APP_EVENT_FLAGS_CREATE(
+			      APP_EVENT_TYPE_FLAGS_INIT_LOG_ENABLE));