Reduces CPU burn by using a typed List to avoid the expensive type
assertions from using an interface. This is the only option for now
until Go makes generics generally available.

The change brings time spent on the time assertion cummulatively to:
    580ms down from 6.88s

Explanation:
The type assertions were showing up heavily in profiles:
* Before this commit
```shell
Total: 42.18s
ROUTINE ======================== github.com/cosmos/cosmos-sdk/store/cachekv.newMemIterator
in /Users/emmanuelodeke/go/src/github.com/cosmos/cosmos-sdk/store/cachekv/memiterator.go
    14.01s     18.87s (flat, cum) 44.74% of Total
         .          .     17:	items      []*kv.Pair
         .          .     18:	ascending  bool
         .          .     19:}
         .          .     20:
         .          .     21:func newMemIterator(start, end []byte, items *list.List, ascending bool) *memIterator {
         .      620ms     22:	itemsInDomain := make([]*kv.Pair, 0, items.Len())
         .          .     23:
         .          .     24:	var entered bool
         .          .     25:
     510ms      870ms     26:	for e := items.Front(); e != nil; e = e.Next() {
     6.85s      6.88s     27:		item := e.Value.(*kv.Pair)
     5.71s      8.19s     28:		if !dbm.IsKeyInDomain(item.Key, start, end) {
     120ms      120ms     29:			if entered {
         .          .     30:				break
         .          .     31:			}
         .          .     32:
         .          .     33:			continue
         .          .     34:		}
         .          .     35:
     820ms      980ms     36:		itemsInDomain = append(itemsInDomain, item)
         .          .     37:		entered = true
         .          .     38:	}
         .          .     39:
         .      1.21s     40:	return &memIterator{
         .          .     41:		start:     start,
         .          .     42:		end:       end,
         .          .     43:		items:     itemsInDomain,
         .          .     44:		ascending: ascending,
         .          .     45:	}
```

and given that the list only uses that type, it is only right to lift the
code from container/list.List, and only modify Element.Value's type.

For emphasis, the code is basically just a retrofit of
container/list/list.go but with a typing, and we'll keep it as is
until perhaps Go1.17 or Go1.18 or when everyone uses Go1.17+ after
generics have landed.

* After this commit
```shell
Total: 45.25s
ROUTINE ======================== github.com/cosmos/cosmos-sdk/store/cachekv.newMemIterator
in /Users/emmanuelodeke/go/src/github.com/cosmos/cosmos-sdk/store/cachekv/memiterator.go
     4.84s      6.77s (flat, cum) 14.96% of Total
         .          .     16:	items      []*kv.Pair
         .          .     17:	ascending  bool
         .          .     18:}
         .          .     19:
         .          .     20:func newMemIterator(start, end []byte, items *kv.List, ascending bool) *memIterator {
         .      330ms     21:	itemsInDomain := make([]*kv.Pair, 0, items.Len())
         .          .     22:
         .          .     23:	var entered bool
         .          .     24:
      60ms      160ms     25:	for e := items.Front(); e != nil; e = e.Next() {
     580ms      580ms     26:		item := e.Value
     3.68s      4.78s     27:		if !dbm.IsKeyInDomain(item.Key, start, end) {
      80ms       80ms     28:			if entered {
         .          .     29:				break
         .          .     30:			}
         .          .     31:
         .          .     32:			continue
         .          .     33:		}
         .          .     34:
     440ms      580ms     35:		itemsInDomain = append(itemsInDomain, item)
         .          .     36:		entered = true
         .          .     37:	}
         .          .     38:
         .      260ms     39:	return &memIterator{
         .          .     40:		start:     start,
         .          .     41:		end:       end,
         .          .     42:		items:     itemsInDomain,
         .          .     43:		ascending: ascending,
         .          .     44:	}
```

Fixes #8810