Merge upstream main (PR #183) — discard classifier-mode-on-quota-gate

Upstream PR #183 ("Adding a classifier mode to quota gate") adds a
classifier path to the pre-refactor quota_gate / composite_gate /
AttributeGate / DispatchGate machinery that this branch removed in
favor of the unified Gate/Verdict model. The PR also stamps a typed
Classification field on InternalRouting alongside the framework's
generic Labels map.

This branch already implements the same functional capability via the
reservation-classifier gate (operator-configurable redis-backed
multi-key in-flight cap that stamps a `class` label), which composes
naturally with the tier-priority RMP and admission gate. There is no
useful payload in PR #183's code beyond what we already have, and its
shape conflicts with the redesigned interfaces.

Resolution: -X ours wholesale, plus re-applying our deletions of the
files PR #183 modified that this branch had already removed
(composite_gate{,_test}.go, quota_gate{,_test}.go,
test/integration/gate_factory_redis_test.go,
test/integration/sortedset_quota_gate_test.go).

Signed-off-by: joeltg <joel@reflection.ai>

Author: joeltg

api/internal_api.go

@@ -5,6 +5,14 @@ import (
 	"fmt"
 )
 
+type QuotaClassification string
+
+const (
+	ClassificationNone     QuotaClassification = ""
+	ClassificationReserved QuotaClassification = "reserved"
+	ClassificationOverflow QuotaClassification = "overflow"
+)
+
 // InternalRouting holds the resolved, authoritative routing fields used by
 // infrastructure (producers, workers, retry logic). These are not part of the
 // caller-facing contract and should not be set by callers directly.