feat: add miner_ RPC namespace matching geth-bsc MinerAPI

[constwz]

Summary

Add missing RPC methods to match geth-bsc's API surface, covering the miner_ namespace and two eth_ methods.

1. miner_* RPC Namespace (12 methods)

Reference: bsc/eth/api_miner.go

Fully Functional (shared state with mev_ namespace)

Method	Params	Return	Description
miner_mevRunning	—	bool	Check if validator is accepting MEV bids
miner_startMev	—	()	Enable MEV bid acceptance
miner_stopMev	—	()	Disable MEV bid acceptance (in-flight bids still considered)
miner_addBuilder	address, url	()	Add a builder to the whitelist (url accepted for compat, not used yet)
miner_removeBuilder	address	()	Remove a builder from the whitelist

Informational Error (not applicable in reth-bsc architecture)

These methods return descriptive errors explaining the reth-bsc equivalent configuration approach:

Method	geth-bsc Behavior	reth-bsc Guidance
miner_start	Start mining	Mining lifecycle managed by node configuration
miner_stop	Stop mining	Mining lifecycle managed by node configuration
miner_setExtra	Set block extra data	Extra data managed by Parlia consensus
miner_setGasPrice	Set min gas price	Use BSC_MIN_GAS_TIP env var
miner_setGasLimit	Set gas limit target	Use BSC_GAS_LIMIT env var
miner_setEtherbase	Set validator address	Derived from BSC_PRIVATE_KEY / BSC_KEYSTORE_PATH
miner_setRecommitInterval	Set recommit interval	Not supported

2. eth_coinbase and eth_health

Method	Description
eth_coinbase	Returns configured validator address (replaces reth's default "unimplemented" error)
eth_health	Returns true if the node is healthy (can provide a best block number)

Note: eth_config (EIP-7910) is already provided by reth's EthConfigHandler — no changes needed.

Implementation Details

• Builder whitelist moved to global shared state (shared.rs) so both mev_ and miner_ namespaces operate on the same Arc<RwLock<HashSet<Address>>>
• MEV start/stop exposed via shared::start_mev() / shared::stop_mev() for the miner_ namespace
• eth_coinbase override: uses remove_method_from_configured("eth_coinbase") to remove reth's default unimplemented handler, then registers the BSC implementation
• New files: src/rpc/miner.rs, src/rpc/eth_ext.rs
• Registered in src/main.rs alongside existing parlia, mev, blob RPC modules

Test plan

• cargo check passes
• cargo clippy -p reth_bsc --tests --all-features — no warnings
• Manual test: curl -X POST --data '{"jsonrpc":"2.0","method":"miner_mevRunning","params":[],"id":1}' http://localhost:8545
• Manual test: miner_addBuilder / miner_removeBuilder verify shared state with mev_hasBuilder
• Manual test: eth_coinbase returns validator address instead of "unimplemented" error
• Manual test: eth_health returns true on healthy node

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