to_regex does not support type to be a list of types anymore.

[LorrinWWW]

Describe the issue as clearly as possible:

In the outlines repo, there was method to_regex & build_regex_from_schema that can correctly parse type being a list of types. Recently outlines opted to use outlines-core's implementation and it cannot parse this anymore.

Steps/code to reproduce the bug:

##### outlines==0.1.8 works

import json
from outlines.fsm.json_schema import build_regex_from_schema

schema = {
    "properties": {
        "text": {"type": ["string", "number"]},
    }
}

regex = build_regex_from_schema(json.dumps(schema))

#####

import json
from outlines_core.fsm.json_schema import build_regex_from_schema

schema = {
    "properties": {
        "text": {"type": ["string", "number"]},
    }
}

regex = build_regex_from_schema(json.dumps(schema))

---> 11 regex = build_regex_from_schema(json.dumps(schema))

ValueError: 'type' must be a string

Expected result:

It should be able to parse `dtype` as a list.

Error message:

---> 11 regex = build_regex_from_schema(json.dumps(schema))

ValueError: 'type' must be a string

Outlines/Python version information:

Version information

``` 0.1.8 ```

outlines.fsm.json_schema.build_regex_from_schema was removed in outlines>=0.1.9

Context for the issue:

No response