feat: ADR-040: Implement BadgerDB backend (#9848)

## Description

Partially resolves: https://github.com/vulcanize/cosmos-sdk/issues/14

Implements a [BadgerDB](https://pkg.go.dev/github.com/dgraph-io/badger/v3)-based backend for the DB interface introduced by https://github.com/cosmos/cosmos-sdk/pull/9573 and specified by [ADR-040](https://github.com/cosmos/cosmos-sdk/blob/eb7d939f86c6cd7b4218492364cdda3f649f06b5/docs/architecture/adr-040-storage-and-smt-state-commitments.md). This uses Badger's "managed" mode for version management, and supports optimistically concurrent transactions (required one [patch](https://github.com/dgraph-io/badger/pull/1716) upstream to fix handling of write conflicts).

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules) - n/a
- [x] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [x] added a changelog entry to `CHANGELOG.md`
- [x] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [x] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

db/dbtest/testcases.go

@@ -369,16 +369,19 @@ func DoTestReloadDB(t *testing.T, load Loader) {
 	dirname := t.TempDir()
 	db := load(t, dirname)
 
-	txn := db.Writer()
-	for i := 0; i < 100; i++ {
-		require.NoError(t, txn.Set(ikey(i), ival(i)))
-	}
-	require.NoError(t, txn.Commit())
-	first, err := db.SaveNextVersion()
-	require.NoError(t, err)
+	var firstVersions []uint64
 
-	txn = db.Writer()
-	for i := 0; i < 50; i++ { // overwrite some values
+	for i := 0; i < 10; i++ {
+		txn := db.Writer()
+		require.NoError(t, txn.Set(ikey(i), ival(i)))
+		require.NoError(t, txn.Commit())
+		ver, err := db.SaveNextVersion()
+		require.NoError(t, err)
+		firstVersions = append(firstVersions, ver)
+	}
+
+	txn := db.Writer()
+	for i := 0; i < 5; i++ { // overwrite some values
 		require.NoError(t, txn.Set(ikey(i), ival(i*10)))
 	}
 	require.NoError(t, txn.Commit())
@@ -386,45 +389,51 @@ func DoTestReloadDB(t *testing.T, load Loader) {
 	require.NoError(t, err)
 
 	txn = db.Writer()
-	for i := 100; i < 150; i++ {
-		require.NoError(t, txn.Set(ikey(i), ival(i)))
-	}
+	require.NoError(t, txn.Set(ikey(100), ival(100)))
 	require.NoError(t, txn.Commit())
-	db.Close()
 
 	// Reload and check each saved version
+	db.Close()
 	db = load(t, dirname)
 
-	view, err := db.ReaderAt(first)
+	// require.True(t, db.Versions().Equal(versions))
+	vset, err := db.Versions()
 	require.NoError(t, err)
-	for i := 0; i < 100; i++ {
-		v, err := view.Get(ikey(i))
-		require.NoError(t, err)
-		require.Equal(t, ival(i), v)
-	}
-	view.Discard()
+	require.Equal(t, last, vset.Last())
 
-	view, err = db.ReaderAt(last)
-	require.NoError(t, err)
-	for i := 0; i < 50; i++ {
-		v, err := view.Get(ikey(i))
-		require.NoError(t, err)
-		require.Equal(t, ival(i*10), v)
+	txn = db.Writer()
+	for i := 10; i < 15; i++ {
+		require.NoError(t, txn.Set(ikey(i), ival(i+10)))
 	}
-	for i := 50; i < 100; i++ {
+	require.NoError(t, txn.Commit())
+
+	for i := 0; i < 10; i++ {
+		view, err := db.ReaderAt(firstVersions[i])
+		require.NoError(t, err)
+		val, err := view.Get(ikey(i))
+		require.NoError(t, err)
+		require.Equal(t, ival(i), val)
+		view.Discard()
+	}
+
+	view, err := db.ReaderAt(last)
+	require.NoError(t, err)
+	for i := 0; i < 10; i++ {
 		v, err := view.Get(ikey(i))
 		require.NoError(t, err)
-		require.Equal(t, ival(i), v)
+		if i < 5 {
+			require.Equal(t, ival(i*10), v)
+		} else {
+			require.Equal(t, ival(i), v)
+		}
 	}
 	view.Discard()
 
 	// Load working version
 	view = db.Reader()
-	for i := 100; i < 150; i++ {
-		v, err := view.Get(ikey(i))
-		require.NoError(t, err)
-		require.Equal(t, ival(i), v)
-	}
+	val, err := view.Get(ikey(100))
+	require.NoError(t, err)
+	require.Equal(t, ival(100), val)
 	view.Discard()
 
 	require.NoError(t, db.Close())