fix(rpc): make eth_maxPriorityFeePerGas return tx_gas_price instead of a constant 0 (#5653)
Problem
eth_maxPriorityFeePerGas is hard-coded to 0x0
(EthEndpoint::maxPriorityFeePerGas), and every block reports
baseFeePerGas = 0x0 (BlockResponse.cpp). A client that prices an
EIP-1559 transaction the standard way, `maxFeePerGas = 2 * baseFeePerGas

maxPriorityFeePerGas, therefore computes maxFeePerGas = 0. TxValidator(FIB-75) then rejects the transaction becauseeffectiveGasPrice(tx) < tx_gas_price, and reports it as InsufficientFunds` — which sends the user hunting for balance they
already have.

Reproduced on the POTOS testnet (v3.17.1, tx_gas_price = 0x5208) from
the same account and nonce:
eth_gasPrice                -> 0x5208   (21000 wei)
eth_maxPriorityFeePerGas    -> 0x0
latest.baseFeePerGas        -> 0x0

type-2 tx, maxFeePerGas=1      -> {"code":-32603,"message":"InsufficientFunds"}
type-2 tx, maxFeePerGas=42000  -> accepted, 0x5d8047e8…e4a172
web3j DynamicEIP1559GasProvider, ethers getFeeData() and viem
estimateFeesPerGas() all use that formula, so any EIP-1559 sender that
trusts the node’s own fee hints is rejected. Only clients that ignore
the 1559 hints and take eth_gasPrice get through.
Fix
Since the base fee is always reported as 0, the whole system gas price
is the tip. eth_maxPriorityFeePerGas now returns the tx_gas_price
system config, the same value eth_gasPrice returns, so 2 * 0 + tip
lands exactly on the admission floor. The two endpoints share a new
private helper systemGasPriceQuantity(); eth_gasPrice behaviour is
unchanged.
The value charged at execution is tx_gas_price regardless of
maxFeePerGas (BlockExecutive::setEffectiveGasPrice), so a higher
hint costs the sender nothing extra.
Tests

New Web3MaxPriorityFeeTest: with tx_gas_price = 0x5208, both
endpoints return 21000 and the client formula reaches the floor; the tip
follows a config change and drops to 0 when tx_gas_price = 0x0.
Web3NodeStatusTest::maxPriorityFeePerGasIsConstant renamed to
maxPriorityFeePerGasResponds; its assertion (a result or an error is
present) still holds.

Local run: test-bcos-rpc full suite, see below.