[ISSUE] warehouses.list() silently drops warehouse_type for warehouse types not in the SDK enum

[phongl7]

Description

WorkspaceClient.warehouses.list() (and .get()) returns EndpointInfo objects whose warehouse_type is missing entirely when the server returns a warehouse type value that isn't one of the three the SDK's enum knows about. We hit this with the real-time SQL warehouse type (REAL_TIME): the REST API returns a warehouse_type, but warehouse.as_dict() has no warehouse_type key at all.

This is silent data loss — the field the server sent just disappears, with no error or warning.

Reproduction

from databricks.sdk.service.sql import EndpointInfo

# What the REST API returns for the real-time warehouse type (newer than the SDK's enum):
ei = EndpointInfo.from_dict({"id": "abc", "name": "shared-real-time", "warehouse_type": "REAL_TIME"})

print(ei.warehouse_type)            # -> None
print("warehouse_type" in ei.as_dict())   # -> False   (field is gone)

Root cause

EndpointInfoWarehouseType only defines CLASSIC, PRO, TYPE_UNSPECIFIED
(databricks/sdk/service/sql.py). Deserialization goes through _enum()
(databricks/sdk/service/_internal.py):

def _enum(d, field, cls):
    """Unknown enum values are returned as None."""
    ...
    return _get_enum_value(cls, d[field])   # returns None for any unknown value

as_dict() then omits None fields (if self.warehouse_type is not None), so an
unknown enum value is lost completely — not even the raw string survives.

There are really two problems:

1. Missing enum value — EndpointInfoWarehouseType (and GetWarehouseResponseWarehouseType) need REAL_TIME. Since sql.py is code-generated (DO NOT EDIT), this has to be fixed in the upstream OpenAPI spec.
2. Silent data loss for any unknown enum — even once the spec catches up, the SDK will keep dropping any future server-side enum value it doesn't recognize. This affects every enum field SDK-wide, not just warehouses.

Expected behavior

Unknown enum values returned by the server should be preserved, not silently dropped, so that as_dict() reflects what the API actually returned.

Proposed fix

For (2), preserve unknown values via a small wrapper in _internal.py that still
round-trips through as_dict() (which calls .value), while remaining
distinguishable from a known enum member.
PR: #1485

For (1), the enum value needs to be added in the spec.