Fix some common anti-patterns with these data structures.

- You can dereference the iterator returned by `find` to access the
  underlying value directly, without an extra `operator[]`/`at`.
- Rather than checking for an element before insertion/deletion, you can
  just do the operation and if needed check the return value to
  determine if the insertion/deletion succeeded.

Update clang-format to version 19

find ./Source/ -name '*.cpp' -o -name '*.h' | xargs clang-format-19 -i

Found via `codespell -q 3 -S "./Externals,./Data/Sys/wiitdb-??.txt,*.po,*.pot" -L andf,asnd,bootup,brocken,bufferin,clen,collet,datas,delt,diety,extint,fpr,inout,inport,interm,nd,nin,ontop,pixelx,re-use,re-used,sav,stateman,strat,transer,wil`