Reland "Get rid of tail padding within `absl::Duration`. This reduces memory usage needs when storing duration in containers (e.g. `vector<absl::Duration>` uses 25% less memory), and allows classes with `absl::Duration` fields to fit other stuff in memory previously used by tail padding (e.g. `std::optional<absl::Duration>` is now 16 bytes instead of 24)."

PiperOrigin-RevId: 524256689
Change-Id: Ibf40d9e5411020179fa34c972349c7b58aa9d908