Improve caching (#19130)

* Remove lock for cached operations.
* Rename "Relax" to `ReturnLastGood`.
* Add `CacheError` to allow caching values even on errors.
* Add NoWait that will return current value with async fetching if within 2xTTL.
* Make benchmark somewhat representative.

```
Before: BenchmarkCache-12       16408370                63.12 ns/op            0 B/op
After:  BenchmarkCache-12       428282187                2.789 ns/op           0 B/op
```

* Remove `storageRESTClient.scanning`. Nonsensical - RPC clients will not have any idea about scanning.
* Always fetch remote diskinfo metrics and cache them. Seems most calls are requesting metrics.
* Do async fetching of usage caches.

internal/cachevalue/cache_test.go

@@ -51,7 +51,7 @@ func TestCache(t *testing.T) {
 func BenchmarkCache(b *testing.B) {
 	cache := New[time.Time]()
 	cache.Once.Do(func() {
-		cache.TTL = 1 * time.Microsecond
+		cache.TTL = 1 * time.Millisecond
 		cache.Update = func() (time.Time, error) {
 			return time.Now(), nil
 		}