Support recursive in get-in

Hi,

it seems recursive is not supported by get-in. Was it omitted on purpose?
With small modifications it works for my use case:

```
(defn- unwrap-recursive [m]
(cond
(recursive? m) (deref (:derefable m)) ; probably use schema-value
:else m))
```

```
(defn- get-in-schema [m k & [default]]
(unwrap-recursive (unwrap-sequence-schemas (get m (key-in-schema m k) default))))

```

Start by tracing the existing get-in behavior and the shown get-in-schema, unwrap-recursive, and unwrap-sequence-schemas functions. Read how recursive?, :derefable, and schema-value are handled elsewhere in the project. Done means get-in supports recursive schemas consistently with the existing schema unwrapping behavior, with coverage for the reported use case.

Written by the indexing model from the issue text.