feat(flowcontrol): add VTC fairness policy with token-based cost and starvation prevention

Signed-off-by: Guangya Liu <gyliu513@gmail.com>

Author: gyliu513

cmd/epp/runner/runner.go

@@ -73,6 +73,7 @@ import (
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/globalstrict"
 	programaware "github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/program-aware"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/roundrobin"
+	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/vtc"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/ordering/edf"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/ordering/fcfs"
 	slodeadline "github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/ordering/slodeadline"
@@ -588,6 +589,7 @@ func (r *Runner) registerInTreePlugins() {
 	fwkplugin.Register(globalstrict.GlobalStrictFairnessPolicyType, globalstrict.GlobalStrictFairnessPolicyFactory)
 	fwkplugin.Register(roundrobin.RoundRobinFairnessPolicyType, roundrobin.RoundRobinFairnessPolicyFactory)
 	fwkplugin.Register(programaware.ProgramAwarePluginType, programaware.ProgramAwarePluginFactory)
+	fwkplugin.Register(vtc.VTCFairnessPolicyType, vtc.VTCFairnessPolicyFactory)
 	fwkplugin.Register(fcfs.FCFSOrderingPolicyType, fcfs.FCFSOrderingPolicyFactory)
 	fwkplugin.Register(edf.EDFOrderingPolicyType, edf.EDFOrderingPolicyFactory)
 	fwkplugin.Register(slodeadline.SLODeadlineOrderingPolicyType, slodeadline.SLODeadlineOrderingPolicyFactory)

pkg/epp/framework/plugins/flowcontrol/fairness/functional_test.go

@@ -28,6 +28,7 @@ import (
 	fwkplugin "github.com/llm-d/llm-d-router/pkg/epp/framework/interface/plugin"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/globalstrict"
 	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/roundrobin"
+	"github.com/llm-d/llm-d-router/pkg/epp/framework/plugins/flowcontrol/fairness/vtc"
 )
 
 // TestFairnessPolicyConformance is the main conformance test suite for FairnessPolicy implementations.
@@ -39,6 +40,7 @@ func TestFairnessPolicyConformance(t *testing.T) {
 	policies := map[string]fwkplugin.FactoryFunc{
 		globalstrict.GlobalStrictFairnessPolicyType: globalstrict.GlobalStrictFairnessPolicyFactory,
 		roundrobin.RoundRobinFairnessPolicyType:     roundrobin.RoundRobinFairnessPolicyFactory,
+		vtc.VTCFairnessPolicyType:                   vtc.VTCFairnessPolicyFactory,
 	}
 
 	for name, f := range policies {