build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

backend/cache/storage_persistent.go

@@ -607,16 +607,16 @@ func (b *Persistent) CleanChunksBySize(maxSize int64) {
 }
 
 // Stats returns a go map with the stats key values
-func (b *Persistent) Stats() (map[string]map[string]interface{}, error) {
-	r := make(map[string]map[string]interface{})
-	r["data"] = make(map[string]interface{})
+func (b *Persistent) Stats() (map[string]map[string]any, error) {
+	r := make(map[string]map[string]any)
+	r["data"] = make(map[string]any)
 	r["data"]["oldest-ts"] = time.Now()
 	r["data"]["oldest-file"] = ""
 	r["data"]["newest-ts"] = time.Now()
 	r["data"]["newest-file"] = ""
 	r["data"]["total-chunks"] = 0
 	r["data"]["total-size"] = int64(0)
-	r["files"] = make(map[string]interface{})
+	r["files"] = make(map[string]any)
 	r["files"]["oldest-ts"] = time.Now()
 	r["files"]["oldest-name"] = ""
 	r["files"]["newest-ts"] = time.Now()