cache namespace in record-maintainer

[dannypsnl]

Is your feature request related to a problem? Please describe.
Every modification will invoke a slow expanding, but this can be avoided by reusing namespace.

Describe the solution you'd like
The current ns (make-base-namespace) is defined in function collect-from path, a better way is maintaining it in record-maintainer, which is a thread for each single racket module.

Describe alternatives you've considered
No

Additional context
According to jeapostrophe/racket-langserver#135, cache namespace will make a huge speed up.