use testhook auditor to track Qcx open/close

This also requires doing something to keep the TxGroup in each Qcx
from holding its Tx references after the Qcx closes, because otherwise
the list of Qcxs that we keep to verify that they all got closed ends
up keeping every shared/read-only Tx open forever, resulting in many
gigabytes of memory usage when running with the race detector.  To
avoid having to reason about whether anything would ever access a nil
TxGroup, or run through iteratively zeroing maps, we just make a new
empty group at that point.

txfactory.go

@@ -31,6 +31,7 @@ import (
 	"github.com/molecula/featurebase/v2/roaring"
 	txkey "github.com/molecula/featurebase/v2/short_txkey"
 	"github.com/molecula/featurebase/v2/storage"
+	"github.com/molecula/featurebase/v2/testhook"
 	. "github.com/molecula/featurebase/v2/vprint" // nolint:staticcheck
 	"github.com/pkg/errors"
 	"github.com/zeebo/blake3"
@@ -147,6 +148,11 @@ func (q *Qcx) Finish() (err error) {
 		}
 	}
 	err2 := q.Grp.FinishGroup()
+	// drop the old group so we aren't holding references to all those Tx
+	q.Grp = q.Txf.NewTxGroup()
+	if !q.done {
+		_ = testhook.Closed(q.Txf.holder.Auditor, q, nil)
+	}
 	q.done = true
 
 	if err != nil {
@@ -164,7 +170,11 @@ func (q *Qcx) Abort() {
 		(*q.RequiredForAtomicWriteTx).Rollback()
 	}
 	q.Grp.AbortGroup()
-
+	// drop the old group so we aren't holding references to all those Tx
+	q.Grp = q.Txf.NewTxGroup()
+	if !q.done {
+		_ = testhook.Closed(q.Txf.holder.Auditor, q, nil)
+	}
 	q.done = true
 }
 
@@ -197,6 +207,7 @@ func (f *TxFactory) NewQcx() (qcx *Qcx) {
 	if f.typeOfTx == "roaring" {
 		qcx.isRoaring = true
 	}
+	_ = testhook.Opened(f.holder.Auditor, qcx, nil)
 	return
 }