[C#] Support for format `date-time-local` to generate type `DateTime`

### Is your feature request related to a problem? Please describe the problem.

Currently when an OpenAPI spec specifies a property with the format [date-time-local](https://spec.openapis.org/registry/format/date-time-local.html)
e.g.
```json
"properties": {
"foo": {
"type": "string",
"format": "date-time-local"
}
}
```
It will generate a property with type `string`:
```C#
public string Foo { get; set; }
```

### Client library/SDK language

Csharp

### Describe the solution you'd like

Generate the property to type `DateTime`:
```C#
public string DateTime { get; set; }
```

### Additional context

_No response_

Start by tracing the C# generator's handling of OpenAPI string formats and its existing date-time mapping. Add support for the `date-time-local` format so the generated property uses `DateTime`, then verify that the example schema no longer produces a `string` property.

Written by the indexing model from the issue text.