accounting: fix memory leak from stats groups on long-running rcd

Before this change, `NewStats` stored the context it was created from on the
`StatsInfo`. Stats groups are never freed -- they are only evicted once there are
`--max-stats-groups` of them -- so each one kept its context, and everything reachable
from it, alive for the life of the process. As the rc creates a group per call,
that included the call's filters and their compiled regexps.

The context was only ever used to get `ci.StatsFileNameLength` from the config.
`StatsInfo` already stores that same `*fs.ConfigInfo`, read from the same
context in `NewStats`.

This change fixes the issue by passing the stored ci to `transferMap.String` and
dropping the context from `StatsInfo`.

fs/accounting/stats.go

@@ -33,7 +33,6 @@ var MaxCompletedTransfers = 100
 // to correctly count the updated fields
 type StatsInfo struct {
 	mu                    sync.RWMutex
-	ctx                   context.Context
 	ci                    *fs.ConfigInfo
 	bytes                 int64
 	errors                int64
@@ -85,7 +84,6 @@ type averageValues struct {
 func NewStats(ctx context.Context) *StatsInfo {
 	ci := fs.GetConfig(ctx)
 	s := &StatsInfo{
-		ctx:                   ctx,
 		ci:                    ci,
 		checking:              newTransferMap(ci.Checkers, "checking"),
 		transferring:          newTransferMap(ci.Transfers, "transferring"),
@@ -518,10 +516,10 @@ func (s *StatsInfo) String() string {
 	// Add per transfer stats if required
 	if !s.ci.StatsOneLine {
 		if !s.checking.empty() {
-			_, _ = fmt.Fprintf(buf, "Checking:\n%s\n", s.checking.String(s.ctx, s.inProgress, s.transferring))
+			_, _ = fmt.Fprintf(buf, "Checking:\n%s\n", s.checking.String(s.ci, s.inProgress, s.transferring))
 		}
 		if !s.transferring.empty() {
-			_, _ = fmt.Fprintf(buf, "Transferring:\n%s\n", s.transferring.String(s.ctx, s.inProgress, nil))
+			_, _ = fmt.Fprintf(buf, "Transferring:\n%s\n", s.transferring.String(s.ci, s.inProgress, nil))
 		}
 	}
 

fs/accounting/transfermap.go

@@ -1,7 +1,6 @@
 package accounting
 
 import (
-	"context"
 	"fmt"
 	"maps"
 	"sort"
@@ -91,10 +90,9 @@ func (tm *transferMap) _sortedSlice() []*Transfer {
 
 // String returns string representation of map items excluding any in
 // exclude (if set).
-func (tm *transferMap) String(ctx context.Context, progress *inProgress, exclude *transferMap) string {
+func (tm *transferMap) String(ci *fs.ConfigInfo, progress *inProgress, exclude *transferMap) string {
 	tm.mu.RLock()
 	defer tm.mu.RUnlock()
-	ci := fs.GetConfig(ctx)
 	stringList := make([]string, 0, len(tm.items))
 	for _, tr := range tm._sortedSlice() {
 		var what = tr.what