Preserve line breaks across a parse(stringify()) round-trip

[mahirhir]

stringify escapes a line break to the two characters \n and wraps the value in double quotes, but parse strips the quotes without reversing that escape. A value that contains a line break therefore does not survive a round-trip through the library's own functions:

const { parse, stringify } = require('envfile')

parse(stringify({ greeting: 'hello\nworld' }))
// => { greeting: 'hello\\nworld' }   a literal backslash-n, not a line break

The two existing tests show the intent. "line breaks inside quotes should be preserved on parse" feeds parse an actual line break inside quotes, and "...on stringify" checks that stringify emits the escaped \n form. They were only ever checked in isolation, so composing them silently drops the line break.

parse is the inverse of stringify, so it should reverse what stringify produces. This makes removeQuotes unescape \n back to a line break for double-quoted values, which matches dotenv's double-quote semantics where \n denotes a line break. Single-quoted values are left raw, as in dotenv.

All existing tests still pass unchanged. I added one that runs parse(stringify(value)) for a value with a line break; reverting the one-line change in removeQuotes makes only that new test fail, with the literal backslash-n shown above.