FastMarshalJSON avoids one of the extra allocations that time.MarshalJSON is making.

GetTimestamp tries to parse given string as RFC3339 time or Unix timestamp (with seconds precision), if successfulreturns a Unix timestamp as string otherwise returns value back.

JSONFormat is the format used by FastMarshalJSON.

RFC3339NanoFixed is our own version of RFC339Nano because we want one that pads the nano seconds part with zeros to ensure the timestamps are aligned in the logs.