Minor improvements for SIMDWrapper / zipping / event model

A few assorted fixes/improvements I came across while doing other things:

• LHCb::Pr::Fitted::Forward::Tracks: throw an exception instead of segfaulting if the ancestor relations are null
• SIMDWrapper: add a constexpr static std::size_t size() { ... } to sse::mask_v for consistency with other backends
• Zipping: change is_proxy_v<T> to not depend on an explicit is_proxy static variable
• Add std::any -> <any> to list of known headers

Should be tested with Rec!2141 (merged) and Moore!577 (merged)

cc: @apearce @mvesteri @nnolte

added Core Event model labels

mentioned in merge request Rec!2141 (merged)

mentioned in merge request Moore!577 (merged)

changed the description

assigned to @abrearod

@olupton please, let me know when this 3 MR are ready to be tested. I see that the pipeline failed in the Moore one, but apparently this is not a problem.

They are ready to be tested, thanks!

• [2020-07-23 12:01] Validation started with lhcb-master-mr#1106
• [2020-07-24 14:24] Validation started with lhcb-master-mr#1110

assigned to @jonrob and unassigned @abrearod

merged

mentioned in commit 0b3cdf77

unassigned @jonrob

mentioned in issue Moore#200 (closed)

added Utilities label and removed Core label

added enhancement label