Add experimental RoaringLookupResources to the Materialize API

[josephschorr]

What this adds

ExperimentalRoaringLookupResources, a new experimental RPC in authzed.api.materialize.v0: given a resource type, a permission, and a subject, it returns a roaring64 bitmap of the IDs of every resource of that type on which the subject has the permission.

The bitmap is serialized in the RoaringFormatSpec 64-bit portable format, which is what OpenSearch consumes directly via a terms query with "value_type": "bitmap" on long fields (once Base64-encoded), and what Java's Roaring64NavigableMap.deserializePortable() reads. Integrators can attach the permission set to each search query instead of replicating access data into the search index and keeping it in sync.

API shape

• Request: a standard Consistency block, resource_object_type, permission, and a SubjectReference — one subject per request.
• Response: the serialized bitmap, its cardinality, and the ZedToken (at_revision) at which the lookup was performed, so callers can thread the same snapshot through subsequent requests.

Constraints, documented on the RPC

• Every resource object ID of the requested type must parse as a canonical-decimal uint64. Any that does not fails the call with FAILED_PRECONDITION rather than returning a partial bitmap — a bitmap that is quietly too small is a wrong authorization answer. Canonical matters: document:007 and document:7 are distinct objects that both parse to 7.
• When a permission relates a type to itself (e.g. group#member looked up for a group#member subject), the subject is one of its own resources, so its object ID is held to the same rule.
• The whole bitmap returns in one unary message. Dense IDs are nearly free, but sparse IDs cost close to 10 bytes each, so large sparse results can exceed the default 4 MiB client-side gRPC receive limit; the doc comment tells callers how to raise it. No server-side result limit is applied.

Naming

Follows the existing convention in this package (ExperimentalCountRelationshipsByFilter in RelationshipsService): the RPC and its messages carry the Experimental prefix; the API is subject to change or removal.

buf lint, buf format, and buf build are clean.

[vroldanbet]

LGTM

[tstirrat15]

LGTM