and make `unpack` return a StatusCode to know when an unpacker has
failed, in which case, if available, another unpacker for the same
CLID can be tried

TrackPacker: Explicitly save packing version to stream buffer, and use correct method to check packing version where needed

Sebastien Ponce authored 3 years ago and Rosen Matev committed 3 years ago

On the way, a PackerBase class was created to host common code and some
cleanup was also performed

* prefer std::abs over fabs
* convert {Un,}PackPrimaryVertices, {PVToRec,RecToPV}Converter to Gaudi::Functional
* prefer Gaudi::Property over declareProperty
* prefer range-based loops

* unify function names to allow the code that uses them
  be more generic
* prefer generic functions over cut-paste-modified code
* use emplace_back the way it is intended
* prefer fmt::format over std::stringstream
* prefer Gaudi::Property
* prefer switch over repeated if

The intention being to measure the impact (if any) on throughput with a
modern compiler

* and remove all instances of StandardPacker

* amalgamate component headers into their corresponding source files
* do not mention SmartRef<T> type when it is not neccessary

This reverts commit 63246e4b.

This will allow to drop by half the number of memory allocations in the Reconstruction code, leading to substancial speedup (we spend 15% of the time allocating/deallocating)

see gaudi/Gaudi!514