Release 5.1.0

[TheJokr]

New Features

• The set_span_finish_callback! macro allows associating a callback with a span. The callback runs when the span is dropped. Children inherit their parent span's callback on creation, but it can be removed explicitly with set_span_finish_callback!(None);. This is intended to simplify the addition of common tags to a whole tree of spans. (Add set_span_finish_callback macro to telemetry::tracing #140)

Improvements

• Spans that are neither sampled nor subject to liveness tracking are replaced by a sentinel value. For production services, these constitute the vast majority of spans. The creation of such spans does not allocate anymore, which is expected to reduce tracing overhead significantly. (Add a new SharedSpanHandle::Inactive variant #144)
• foundations now properly recompiles if its seccomp.h template changed. (Fix rerun directive issuance for build inputs #143)