feat(bar): 按间隔节流 bar_item 更新

- 新增 base/time: time_monotonic_ms 与 time_create_monotonic_timerfd_by_fps
- bar 初始化改用该工具创建 timerfd，移除内联的 itimerspec 拼装
- bar_item_update 按 update_interval_ms 节流，记录 last_updated_time 跳过过早更新

src/base/time.c

@@ -0,0 +1,56 @@
+#include "base/time.h"
+
+#include <bits/time.h>
+#include <bits/types/struct_itimerspec.h>
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/timerfd.h>
+#include <time.h>
+
+#include "base/log.h"
+
+static int time_create_monotonic_timerfd(const struct itimerspec *itimerspec) {
+  auto timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC);
+  if (timerfd == -1) {
+    auto err = errno;
+    warn("time_create_timerfd failed: %s", strerror(err));
+    return timerfd;
+  }
+
+  timerfd_settime(timerfd, 0, itimerspec, nullptr);
+  return timerfd;
+}
+
+static constexpr auto NANOSECONDS_OF_ONE_SECOND = 1'000'000'000ULL;
+
+int time_create_monotonic_timerfd_by_fps(uint32_t fps) {
+  if (fps == 0) fps = 30;
+
+  auto interval_ns = NANOSECONDS_OF_ONE_SECOND / fps;
+
+  /* clang-format off */
+  struct itimerspec timer_spec = {
+    .it_value = {
+      .tv_sec  = 0,
+      .tv_nsec = interval_ns % NANOSECONDS_OF_ONE_SECOND,
+    },
+    .it_interval = {
+      .tv_sec  = interval_ns / NANOSECONDS_OF_ONE_SECOND,
+      .tv_nsec = interval_ns % NANOSECONDS_OF_ONE_SECOND,
+    },
+  };
+  /* clang-format on */
+
+  return time_create_monotonic_timerfd(&timer_spec);
+}
+
+static uint64_t time_monotonic_ns(void) {
+  struct timespec timestamp = {0};
+  if (clock_gettime(CLOCK_MONOTONIC, &timestamp) == -1) {
+    warn("clock_gettime failed: %s", strerror(errno));
+  }
+  return timestamp.tv_sec * NANOSECONDS_OF_ONE_SECOND + timestamp.tv_nsec;
+}
+
+uint64_t time_monotonic_ms(void) { return time_monotonic_ns() / 1'000'000U; }

src/base/time.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <stdint.h>
+
+int time_create_monotonic_timerfd_by_fps(uint32_t fps);
+uint64_t time_monotonic_ms(void);