Private IPv4 mapped regions are only matched in dot-notation

The `isPrivate` function only matches IPv4 mapped addresses in compacted dot-notation.

## Example
```js
var ip = require("ip")

console.log(ip.isPrivate("::ffff:127.0.0.1"))
console.log(ip.isPrivate("::ffff:7f00:0001"))
console.log(ip.isPrivate("0:0:0:0:0:ffff:127.0.0.1"))
console.log(ip.isPrivate("0:0:0:0:0:ffff:7f00:0001"))
```

### Expected
```js
true
true
true
true
```

### Actual
```js
true
false
false
false
```

Start by locating the isPrivate function in the node-ip source and trace how IPv4-mapped IPv6 addresses are parsed and compared. Reproduce the four examples from the issue, then add coverage for the compacted and expanded forms and confirm all expected results pass in the existing test suite.

Written by the indexing model from the issue text.