Connect to unix domain socket using short syntax.

I've tried two variants:
```ts
const db = await mongo.connect("mongodb:///tmp/mongodb-27017.sock/mydb");
// Error: MongoError: "Connection failed: Cannot read properties of undefined (reading 'includes')"
```
and
```ts
const db = await mongo.connect("mongodb://%2Ftmp%2Fmongodb-27017.sock/mydb");
// Error: MongoError: "Connection failed: failed to lookup address information: Name or service not known"
```

What is the correct syntax?

Start by reproducing both mongo.connect(...) examples from the issue and compare their errors. Trace the connection-string parsing and Unix-socket handling reached by these calls; done means establishing the intended short-syntax behavior or documenting the supported syntax and adding a regression test if the parser is changed.

Written by the indexing model from the issue text.