gs-common/modem: clock manager interface

A lot of modem code requires sleeping while vendor services do some
background processing. Since we don't want to actually sleep for unit
tests, an interface is provided here so that a fake sleep can be
injected.

Test: N/A. Directly forwards methods or does nothing.
Bug: 302435001
Change-Id: I3bcf0307156d93756d69cd9f749c88b508ba9466

modem/clock_manager/include/clock_manager.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <cstddef>
+
+namespace pixel_modem {
+
+/**
+ * @brief Interface for time based operations.
+ *
+ * This interface was intentionally not called `Clock`, like the Java side
+ * counterpart since it's likely that clients would call the local variable
+ * `clock(_)`, which would clash with the C defined `clock` method.
+ */
+struct ClockManager {
+  virtual ~ClockManager() = default;
+
+  /**
+   * @brief Sleep the thread for a given number of seconds.
+   *
+   * @param seconds Minimum number of seconds to sleep for. Note, this is
+   * different than the Java android clock which accepts seconds. This was done
+   * because C++ developers are likely more familiar with the `sleep` command,
+   * which accepts seconds.
+   */
+  virtual void Sleep(size_t seconds) const = 0;
+};
+
+}  // namespace pixel_modem