Override clock fields in copied traces

Override clock fields in copied traces

Some tracers like LTTng use a compression scheme on the timestamp field
to avoid writing the full 64-bit timestamp at every event. When the
trace is complete, the reader has all the information to understand this
compression, but if a trace is filtered or truncated, there might be
some state information missing.

Since we don't know in advance if a compression scheme is used in a
trace, we now force the copied traces to have a full 64-bit timestamp.

The user of this library can decide whether or not to override the type
of the clock fields.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>