Problem: tx is not replaced by priority

Closes: #1557

Solution:
- add TxReplacement callback, only replace if priority is higher

CHANGELOG.md

@@ -31,6 +31,7 @@
 * (store) [#1526](https://github.com/crypto-org-chain/cronos/pull/1526) Cache index/filters in rocksdb application.db to reduce ram usage.
 * (store)[#1529](https://github.com/crypto-org-chain/cronos/pull/1529) Enable pinL0FilterAndIndexBlocksInCache.
 * (store)[#1547](https://github.com/crypto-org-chain/cronos/pull/1547) Disable memiavl cache if block-stm is enabled.
+* (app) [#]() Only replace tx if new priority is larger.
 
 ### Bug Fixes
 

app/app.go

@@ -375,6 +375,10 @@ func New(
 			TxPriority:      mempool.NewDefaultTxPriority(),
 			SignerExtractor: evmapp.NewEthSignerExtractionAdapter(mempool.NewDefaultSignerExtractionAdapter()),
 			MaxTx:           maxTxs,
+			TxReplacement: func(op, np int64, oTx, nTx sdk.Tx) bool {
+				// tx is only replaced if new priority is higher than old priority
+				return np > op
+			},
 		})
 		handler := baseapp.NewDefaultProposalHandler(mempool, app)