THistSvc: cache TObject types

The TObject::InheritsFrom call can be quite slow. Since we already deduce the object type (TH1, TTree, etc.) during registration, save this information and use it instead of re-deriving it every time. Also avoid calling updateFiles if no TTrees are registered.

Both these changes significantly speed up the EndEvent incident handling for jobs with large (>10k) number of histograms. Thanks to @rbielski for reporting this.

Also re-organize struct THistID to avoid padding (using Pahole), delete unused reset method and include debug message protections from @smh (!1283 (closed)).