lib: refactor some lib/internals

Some light refactoring of internals/*.js

• For linkedlist and freelist, this yields about a 5% perf improvement in general
• Consistent use of the module.exports = {} pattern, with module.exports = {} at the end.

(do not squash commits)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

lib/internal