Performance improvements

[johnkerl]

Done with the help of Cursor.

Before and after: before this PR, and on each commit:

TIME IN SECONDS 413.809 -- ./gocc -o foo1 /Users/kerl/git/johnkerl/miller/pkg/parsing/mlr.bnf
TIME IN SECONDS 321.756 -- ./gocc -o foo2 /Users/kerl/git/johnkerl/miller/pkg/parsing/mlr.bnf
TIME IN SECONDS 226.692 -- ./gocc -o foo3 /Users/kerl/git/johnkerl/miller/pkg/parsing/mlr.bnf
TIME IN SECONDS 155.959 -- ./gocc -o foo4 /Users/kerl/git/johnkerl/miller/pkg/parsing/mlr.bnf
TIME IN SECONDS 135.048 -- ./gocc -o foo5 /Users/kerl/git/johnkerl/miller/pkg/parsing/mlr.bnf

[johnkerl]

Sorry, I meant to push this only to github.com/johnkerl/gocc.