fix!: Fix race condition in mempool blockchain impl

[Eric-Warehime]

Description

Closes: #XXXX

Fixes the following race condition, which is verified when running the included test with the -race flag. As shown in the trace we need to make this thread safe because it can be called from goroutines within the txpool.

758676962391	2025-09-24T01:22:42.391Z	WARNING: DATA RACE
1758676962391	2025-09-24T01:22:42.391Z	Write at 0x00c002156478 by goroutine 327:
1758676962391	2025-09-24T01:22:42.391Z	  github.com/cosmos/evm/mempool.(*Blockchain).NotifyNewBlock()
1758676962391	2025-09-24T01:22:42.391Z	      github.com/cosmos/[email protected]/mempool/blockchain.go:176 +0x337
1758676962391	2025-09-24T01:22:42.391Z	  github.com/cosmos/evm/mempool.(*ExperimentalEVMMempool).SetEventBus.func1()
1758676962391	2025-09-24T01:22:42.391Z	      github.com/cosmos/[email protected]/mempool/mempool.go:399 +0x89
1758676962391	2025-09-24T01:22:42.391Z	  github.com/cosmos/evm/mempool.(*Blockchain).NotifyNewBlock()
1758676962391	2025-09-24T01:22:42.391Z	      github.com/cosmos/[email protected]/mempool/blockchain.go:177 +0x417
...
1758676962393	2025-09-24T01:22:42.393Z	Previous read at 0x00c002156478 by goroutine 191:
1758676962393	2025-09-24T01:22:42.393Z	  github.com/cosmos/evm/mempool.(*Blockchain).StateAt()
1758676962393	2025-09-24T01:22:42.393Z	      <autogenerated>:1 +0x65
1758676962393	2025-09-24T01:22:42.393Z	  github.com/cosmos/evm/mempool/txpool.(*TxPool).loop()
1758676962393	2025-09-24T01:22:42.393Z	      github.com/cosmos/[email protected]/mempool/txpool/txpool.go:191 +0x323
1758676962393	2025-09-24T01:22:42.393Z	  github.com/cosmos/evm/mempool/txpool.New.gowrap1()
1758676962393	2025-09-24T01:22:42.393Z	      github.com/cosmos/[email protected]/mempool/txpool/txpool.go:117 +0x44

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