feat!: change Coin storage model (#9832)

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## Description

Closes: #9361 

<!-- Add a description of the changes that this PR introduces and the files that
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---

### 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
- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [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`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] 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)

types/query/filtered_pagination_test.go

@@ -171,7 +171,7 @@ func (s *paginationTestSuite) TestReverseFilteredPaginations() {
 }
 
 func ExampleFilteredPaginate() {
-	app, ctx, appCodec := setupTest()
+	app, ctx, _ := setupTest()
 
 	var balances sdk.Coins
 	for i := 0; i < numBalances; i++ {
@@ -200,16 +200,16 @@ func ExampleFilteredPaginate() {
 
 	var balResult sdk.Coins
 	pageRes, err := query.FilteredPaginate(accountStore, pageReq, func(key []byte, value []byte, accumulate bool) (bool, error) {
-		var bal sdk.Coin
-		err := appCodec.Unmarshal(value, &bal)
+		var amount sdk.Int
+		err := amount.Unmarshal(value)
 		if err != nil {
 			return false, err
 		}
 
-		// filter balances with amount greater than 100
-		if bal.Amount.Int64() > int64(100) {
+		// filter amount greater than 100
+		if amount.Int64() > int64(100) {
 			if accumulate {
-				balResult = append(balResult, bal)
+				balResult = append(balResult, sdk.NewCoin(string(key), amount))
 			}
 
 			return true, nil
@@ -232,16 +232,16 @@ func execFilterPaginate(store sdk.KVStore, pageReq *query.PageRequest, appCodec
 
 	var balResult sdk.Coins
 	res, err = query.FilteredPaginate(accountStore, pageReq, func(key []byte, value []byte, accumulate bool) (bool, error) {
-		var bal sdk.Coin
-		err := appCodec.Unmarshal(value, &bal)
+		var amount sdk.Int
+		err := amount.Unmarshal(value)
 		if err != nil {
 			return false, err
 		}
 
-		// filter balances with amount greater than 100
-		if bal.Amount.Int64() > int64(100) {
+		// filter amount greater than 100
+		if amount.Int64() > int64(100) {
 			if accumulate {
-				balResult = append(balResult, bal)
+				balResult = append(balResult, sdk.NewCoin(string(key), amount))
 			}
 
 			return true, nil

types/query/pagination_test.go

@@ -319,12 +319,12 @@ func ExamplePaginate() {
 	balancesStore := prefix.NewStore(authStore, types.BalancesPrefix)
 	accountStore := prefix.NewStore(balancesStore, address.MustLengthPrefix(addr1))
 	pageRes, err := query.Paginate(accountStore, request.Pagination, func(key []byte, value []byte) error {
-		var tempRes sdk.Coin
-		err := app.AppCodec().Unmarshal(value, &tempRes)
+		var amount sdk.Int
+		err := amount.Unmarshal(value)
 		if err != nil {
 			return err
 		}
-		balResult = append(balResult, tempRes)
+		balResult = append(balResult, sdk.NewCoin(string(key), amount))
 		return nil
 	})
 	if err != nil { // should return no error