`Client.get_items` has surprising recursive behaviour when using the `/search` endpoint

[mishaschwartz]

The Client.get_items function may get items using the /search endpoint if the server conforms to the ITEM_SEARCH conformance class.

If it does so, the search is always recursive (looks for items in sub-catalogs and sub-collections) even if the recursive=False argument is passed.

I would expect that it would make a non-recursive search instead and only return items that are the immediate child of the current catalog.

Note that the spec recommends that items have a collection as a parent (not a catalog) but catalog parents of items are supported:

• https://github.com/radiantearth/stac-spec/blob/ec002bb93dbfa47976822def8f11b2861775b662/commons/links.md?plain=1#L103
• https://github.com/radiantearth/stac-spec/blob/ec002bb93dbfa47976822def8f11b2861775b662/catalog-spec/catalog-spec.md?plain=1#L74-L75

Additionally, some APIs require that the collections argument be used when using the /search endpoint. This means that this

pystac-client/pystac_client/client.py

Line 460 in 5fae268

search = self.search(ids=ids)

will always raise an APIError for these APIs. This is notably the case for the STAC API at https://planetarycomputer.microsoft.com/api/stac/v1/ which is used in the tests for pystac-client.