mmaprototype: make mmaid local to clusterState

It is included in the datadriven outputs, so having it be global isn't ideal
since then tests change each other's output depending on the order in which
they are run. This wasn't an issue so far - only one trace-producing test ever
calls into rebalanceStores in `mmaprototype` - but that's about to change.

Author: tbg

pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go

@@ -1385,6 +1385,8 @@ type clusterState struct {
 	*constraintMatcher
 	*localityTierInterner
 	meansMemo *meansMemo
+
+	mmaid int // a counter for rebalanceStores calls, for logging
 }
 
 func newClusterState(ts timeutil.TimeSource, interner *stringInterner) *clusterState {

pkg/kv/kvserver/allocator/mmaprototype/cluster_state_rebalance_stores.go

@@ -12,7 +12,6 @@ import (
 	"math/rand"
 	"slices"
 	"strings"
-	"sync/atomic"
 	"time"
 
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
@@ -21,8 +20,6 @@ import (
 	"github.com/cockroachdb/logtags"
 )
 
-var mmaid = atomic.Int64{}
-
 // rebalanceEnv tracks the state and outcomes of a rebalanceStores invocation.
 // Recall that such an invocation is on behalf of a local store, but will
 // iterate over a slice of shedding stores - these are not necessarily local
@@ -117,7 +114,9 @@ type sheddingStore struct {
 func (re *rebalanceEnv) rebalanceStores(
 	ctx context.Context, localStoreID roachpb.StoreID,
 ) []PendingRangeChange {
-	ctx = logtags.AddTag(ctx, "mmaid", mmaid.Add(1))
+	re.mmaid++
+	id := re.mmaid
+	ctx = logtags.AddTag(ctx, "mmaid", id)
 
 	log.KvDistribution.VEventf(ctx, 2, "rebalanceStores begins")
 	// To select which stores are overloaded, we use a notion of overload that