Introduce ReferenceResolver implementing the Package Registry Standard v1.0.0
§5.3 and §4.2:

ReferenceResolver:
- parse(ref_str) → PackageReference handles all three reference schemes
  (registry, ID, local), wrapping ValueError into InvalidPackageReferenceError
- resolve(ref_str) → PackageId resolves references to concrete IDs:
  ID refs directly, registry refs via RegistryClient, local refs reserved
- Integrates with RegistryClient for remote HTTP resolution

Version resolution (§4.2):
- resolve_version(version, available_versions) resolves concrete (vX.Y.Z)
  and mutable aliases (latest, vx, x, vX.x, vX.Y.x)
- is_concrete_version() / is_version_alias() classification helpers

Integration tests: 35 Robot Framework test cases against fake registry server
with version alias resolution support

Benchmarks: 7 ASV benchmark classes covering parse, resolve, and version
resolution across small/medium/large version lists

ISSUES CLOSED: #26

@@ -0,0 +154,4 @@
+        self.resolver = ReferenceResolver()
+        self.registry_ref = "ID:pkg_act_0123456789abcdef0123456789abcdef01234567"
+
+    def time_resolve_registry_ref(self) -> None:

@@ -0,0 +2,4 @@
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator

@@ -0,0 +162,4 @@
+
+    @property
+    def client(self) -> RegistryClient | None:
+        return self._client