Define public API for url_operations

This implements the plan declared at
#613 (comment)

A dedicated list of components is exposed at the package's top-level,
and only that. All other functionality and imports have been move to
package-internal files.

All other, now undesired, top-level imports have been annotated and
scheduled for removal with the v2.0 release.

datalad_next/annexremotes/tests/test_uncurl.py

@@ -14,7 +14,7 @@
     UrlOperationsRemoteError,
     IncompleteResultsError,
 )
-from datalad_next.url_operations.any import AnyUrlOperations
+from datalad_next.url_operations import AnyUrlOperations
 
 from ..uncurl import (
     RemoteError,

datalad_next/annexremotes/uncurl.py

@@ -228,7 +228,7 @@
     UrlOperationsRemoteError,
     UrlOperationsResourceUnknown,
 )
-from datalad_next.url_operations.any import AnyUrlOperations
+from datalad_next.url_operations import AnyUrlOperations
 from datalad_next.utils import ensure_list
 
 from . import (

datalad_next/commands/download.py

@@ -38,7 +38,7 @@
     WithDescription,
 )
 from datalad_next.constraints.dataset import EnsureDataset
-from datalad_next.url_operations.any import AnyUrlOperations
+from datalad_next.url_operations import AnyUrlOperations
 
 lgr = getLogger('datalad.local.download')