Relative `$ref`s are always resolved against root schema path (?)

I'm not sure if it's the intended behaviour, but it feels like it shouldn't be.

`./main.json`:
```json
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"title": "main",
"$ref": "./subdir/child1.json"
}
```

`./subdir/child1.json`:
```json
{
"title": "child1",
"$ref": "../child2.json"
}
```
`./child2.json`:
```json
{
"title": "child2",
"type": "string"
}
```

`wetzel main.json` fails with `Error: Unable to find $ref ../child2.json`, but works if I change the `$ref` in child1 to `./child2.json`, as if child1 is located in the same directory as child2.

Reproduce the failure with main.json, subdir/child1.json, and child2.json using `wetzel main.json`; compare it with the working `./child2.json` reference. Trace the CLI's `$ref` resolution entry point and verify that a reference in child1.json is resolved relative to child1.json's directory, so the command completes successfully.

Written by the indexing model from the issue text.