fix(evm): reject overflow Amount in CheckTx under ForkEVMFixOverflow

[vipwzw]

Problem

EVMContractAction.Amount is uint64, but the underlying chain33 account system uses int64. Amount > math.MaxInt64 wraps to a negative value downstream — the root cause of the fake msg.value attack (0-balance fake deposit draining real funds from bank-style contracts).

ForkEVMFixOverflow (d4ef8c1) already protects the exec layer (CanTransfer rejects overflow, Call/Create revert on Transfer failure, token precompile guarded, transfer-only path guarded). However, CheckTx still performs no amount validation (EvmType.Amount always returns 0, so framework-level checks see nothing), letting such transactions into the mempool and into blocks where they only fail at execution.

Fix

Under ForkEVMFixOverflow, CheckTx now decodes the action and rejects Amount > math.MaxInt64 with types.ErrAmount, so overflow transactions are refused at the mempool / block-check boundary too. Since chain33 runs CheckTx during block execution as well, this keeps malicious txs out of blocks entirely on fork-active chains.

Pre-fork behavior is intentionally unchanged (consensus compatibility).

Tests

New TestCheckTxRejectsAmountOverflow:

• post-fork: MaxUint64 and MaxInt64+1 rejected with ErrAmount
• post-fork: MaxInt64, 1e8, 0 accepted
• pre-fork: MaxUint64 still accepted by CheckTx (historical behavior; exec-layer gate handles it there)

go test -ldflags=-checklinkname=0 ./plugin/dapp/evm/executor/ — all pass (including the existing TestWBTYOverflowAttackIntegration).

[vipwzw]

执行层已经做了拦截（ForkEVMFixOverflow：CanTransfer 的 MaxInt64 守卫、Call/Create 与 transfer-only 路径的 Transfer 返回值检查、token 预编译的 IsInt64 守卫），资金安全已有保障，CheckTx 这个位置不需要额外做拦截。先关闭该 PR。

[vipwzw]

testnode 全链路验证补充（master, ForkEVMFixOverflow 默认生效）：伪充值交易 Amount=MaxUint64 在执行层被 fork gate 拦截后不会上链（QueryTx → tx not exist），攻击者仅损失部署 gas，evm 执行器账户余额为 0，无资金损失可复现。复现测试：plugin-worktrees/master-evm-check 下 plugin/dapp/evm/executor/fake_deposit_testnode_test.go（TestMasterEvmFakeDepositNoFundLoss, PASS）。