refactor(flowcontrol): move the priority queue out of the plugins tree (#2146)

With the queue plugin registry removed (#2036), the priority queue is a
plain internal component of flow control, not a plugin. Move it from
pkg/epp/flowcontrol/framework/plugins/queue to pkg/epp/flowcontrol/queue,
deleting the now-empty pkg/epp/flowcontrol/framework tree so the only
"framework" package left is the plugin SDK at pkg/epp/framework.

Update the flow-control README pillars that still described the deleted
sub-package and the long-removed QueueCapability system.

Signed-off-by: Luke Van Drie <lukevandrie@google.com>

Author: LukeAVanDrie

pkg/epp/flowcontrol/README.md

@@ -99,13 +99,14 @@ their justifications, please refer to the detailed documentation within the rele
     processing loop. It manages a worker that distributes incoming requests, apply policies, and dispatch
     requests to the backends. Its design focuses on high throughput and backpressure.
 
-2.  **Pluggable `Policy` Framework (`./framework`)**: This defines the core interfaces for all pluggable logic. It
-    features a two-tier policy system for `Fairness` (decisions *between* different flows) and `Ordering`
-    (decisions *within* a single flow) logic, covering both request dispatch and displacement.
-
-3.  **Extensible `SafeQueue` System (`./framework`)**: This defines the `framework.SafeQueue` interface for
-    concurrent-safe request storage. It uses a `QueueCapability` system that allows for diverse and extensible queue
-    implementations (e.g., FIFO, Priority Heap) while maintaining a stable interface.
+2.  **Pluggable `Policy` Contracts (`/pkg/epp/framework/interface/flowcontrol`)**: The plugin SDK defines the core
+    interfaces for all pluggable logic. It features a two-tier policy system for `Fairness` (decisions *between*
+    different flows) and `Ordering` (decisions *within* a single flow) logic, covering both request dispatch and
+    displacement.
+
+3.  **The `SafeQueue` (`./contracts`, `./queue`)**: The `contracts.SafeQueue` interface defines concurrent-safe
+    request storage, and `./queue` provides the priority-queue implementation whose dispatch order is determined by
+    the flow's configured `OrderingPolicy`.
 
 4.  **The `FlowRegistry` (`./registry`, `./contracts`)**: This is the stateful control plane of the system. It manages
     the configuration and lifecycle of all flows, policies, and queues. It presents a view of its state to the

…ramework/plugins/queue/benchmark_test.go …/epp/flowcontrol/queue/benchmark_test.gopkg/epp/flowcontrol/framework/plugins/queue/benchmark_test.go renamed to pkg/epp/flowcontrol/queue/benchmark_test.go pkg/epp/flowcontrol/framework/plugins/queue/benchmark_test.go renamed to pkg/epp/flowcontrol/queue/benchmark_test.go

@@ -28,7 +28,7 @@ import (
 
 	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/contracts"
 	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/contracts/mocks"
-	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/framework/plugins/queue"
+	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/queue"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/interface/flowcontrol"
 	fwkfcmocks "github.com/llm-d/llm-d-router/pkg/epp/framework/interface/flowcontrol/mocks"
 )

…framework/plugins/queue/priorityqueue.go …g/epp/flowcontrol/queue/priorityqueue.gopkg/epp/flowcontrol/framework/plugins/queue/priorityqueue.go renamed to pkg/epp/flowcontrol/queue/priorityqueue.go pkg/epp/flowcontrol/framework/plugins/queue/priorityqueue.go renamed to pkg/epp/flowcontrol/queue/priorityqueue.go

@@ -30,7 +30,7 @@ import (
 
 	"github.com/llm-d/llm-d-router/pkg/common/observability/logging"
 	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/contracts"
-	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/framework/plugins/queue"
+	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/queue"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/interface/flowcontrol"
 	"github.com/llm-d/llm-d-router/pkg/epp/metrics"
 )

…work/plugins/queue/priorityqueue_test.go …/flowcontrol/queue/priorityqueue_test.gopkg/epp/flowcontrol/framework/plugins/queue/priorityqueue_test.go renamed to pkg/epp/flowcontrol/queue/priorityqueue_test.go pkg/epp/flowcontrol/framework/plugins/queue/priorityqueue_test.go renamed to pkg/epp/flowcontrol/queue/priorityqueue_test.go

@@ -28,7 +28,7 @@ import (
 	testclock "k8s.io/utils/clock/testing"
 
 	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/contracts"
-	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/framework/plugins/queue"
+	"github.com/llm-d/llm-d-router/pkg/epp/flowcontrol/queue"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/interface/flowcontrol"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/interface/flowcontrol/mocks"
 )