common/peg : refactor until gbnf grammar generation (#24839)

• common/peg : refactor until gbnf grammar into an ac automaton

• cont : add a test with multiple strings

• cont : pad state with 0s so rules line up

• cont : clean up comments

• cont : use set everywhere

• cont : inline state num string padding

• cont : add a ref to PR

• cont : fix regression in server-tools.cpp