iavl: *MutableTree doesn't provide a way to release the database; noticed inside iavl/cmd/iaviewer.ReadTree

[odeke-em]

Noticed while I was working on some potential improvements for iavl/cmd/iaviewer that ReadTree whose code looks like this

iavl/cmd/iaviewer/main.go

Lines 120 to 136 in 172c349

	func ReadTree(dir string, version int, prefix []byte) (*iavl.MutableTree, error) {
	db, err := OpenDB(dir)
	if err != nil {
	return nil, err
	}
	if len(prefix) != 0 {
	db = dbm.NewPrefixDB(db, prefix)
	}
	tree, err := iavl.NewMutableTree(db, DefaultCacheSize, false)
	if err != nil {
	return nil, err
	}
	ver, err := tree.LoadVersion(int64(version))
	fmt.Printf("Got version: %d\n", ver)
	return tree, err
	}

returns *iavl.Mutable https://pkg.go.dev/github.com/cosmos/iavl#MutableTree which doesn't have a way to close the database, but this exhibits an API limitation that .MutableTree needs to return a way to close databases or better, perhaps ReadTree should just take in a database.

[tac0turtle]

want to submit a pr?