perf: only store start offsets for attribute spans

This spares us two usizes per AttrInternal<Range<usize>>.
So on a 64 bit target where a usize is 8 bytes this spares
us 16 bytes of memory per attribute (if spans are enabled,
... for Token<()> this obviously doesn't change anything).

And the DefaultEmitter now also no longer has to update the
spans on each Emitter::push_attribute_(name|value) call.

The spans are now calculated on demand by the Attribute methods,
which is fine since the assumption is that API users are only
interested in a few specific spans (rather than all spans).

0 files changed, 0 insertions, 0 deletions