Port PrLongLivedTracking to Gaudi::Algorithm + misc. changes

• change baseclass to Gaudi::Algorithm
• replace calls to tool<> and svc<> with {Tool,Service}Handle(s)
• replace vector properties which must have a specific length with array properties and avoid intermediate copies
• prefer span as function argument over std::vector
• remove implicit dependency of PrDownTrack on external array of parameters -- instead, force caller to provide those parameters explicitly when PrDownTrack member functions need them.
• remove redundant inline keyword usage