Support parsing `oneof` and `anyof` in params.schema

Hi, I am trying to use `(generate-client *some-symbol* "/path/to/execution-apis/openrpc.json")` (where the api is from https://ethereum.github.io/execution-apis/api-documentation/) to generate a client, but failed because there is `oneOf` keyword in schema of method's params, such as:

```
{
"name": "debug_getRawBlock",
"summary": "Returns an RLP-encoded block.",
"params": [
{
"name": "Block",
"required": true,
"schema": {
"title": "Block number or tag",
"oneOf": [
{
"title": "Block number",
"type": "string",
"pattern": "^0x(0|[1-9a-f][0-9a-f]*)$"
},
{
"title": "Block tag",
"type": "string",
"enum": [
"earliest",
"finalized",
"safe",
"latest",
"pending"
],
"description": "xxxxxxx"
}
]
}
}
],
"result": {
"name": "Block RLP",
"schema": {
"title": "hex encoded bytes",
"type": "string",
"pattern": "^0x[0-9a-f]*$"
}
},
"examples": [
{
"name": "debug_getRawBlock example",
"params": [
{
"name": "Block",
"value": "0x32026E"
}
],
"result": {
"name": "Block RLP",
"value": "xxxxxxx"
}
}
]
},
```

I found it missing schema-to-type method in client/core.lisp, it defaults to get "type" of scheme: https://github.com/40ants/openrpc/blob/d951a3f3d08c02aeb9a33f8e7282266dad5b0b70/client/core.lisp#L131

It would be nice to support paring it. Thanks!

The issue points to client/core.lisp line 131 where schema-to-type method is missing. Look at the OpenRPC spec for 'oneOf' and 'anyOf' handling. The task is to extend the schema parsing logic to support these keywords, likely modifying the type generation. Check existing tests for schema parsing to understand the pattern and add new ones for the union types.

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