feat: reopen() with last input

[llllvvuu]

This saves what the user was working on in the search/replace window so they can come back to it.

It's particularly useful for #13. You can:

1. Do a rough grep e.g. fn to open a quickfix window
2. Do a proper SSR e.g. of fn(a, b)
3. Step through the quickfix window (:cn and :cp keys, :bd key to close buffer) and press the require("ssr").reopen() key for each file.

I tested the cross-buffer/cross-file capability like this:

1. Open large file and do SSR in the middle of the file w/ multiline pattern and multiline template.
2. Close large file
3. Open small file without match and reopen()
4. Open small file with match and reopen()
5. Call replace_confirm() and replace_all() in small file