Tracing receives 0:0 spans when using ScopeTimer

Every ScopeTimer that is constructed inadvertently copy-constructs the tuple members, meaning 1 temporary is created/destructed with no start/stop time. This leaves us with tracing that looks like:

"trace":"request=11472086545592026:543384 get=0:0 bg.wait=11472086545601845:63 get=11472086545596216:18 execute=11472086545592026:23 bg.load=11472086545665306:543241 get=0:0 get=11472087088953283:10 execute=11472087088949455:27"

This affects every get and store as they are the users of ScopeTimer.

A fix (to be checked on all compilers...) is simple to ensure correct construction.

This issue was introduced by https://review.couchbase.org/c/platform/+/166433 and shipped in 7.1.0