fix: run gas-fee and blob-sidecar checks at BidBlock admission time

[chee-chyuan]

Problem

admit_bid_block was missing two of the four checks that go-bsc performs synchronously in preSealVerifyBidBlock before queuing a BidBlock:

#	go-bsc check	Before this PR
1	VerifyUnsealedHeader	deferred (miner-side)
2	BlockTimeUpperCheck	deferred (miner-side)
3	ExtractBidBlockDepositValue + gas-fee validation	missing at admission
4	validateBidBlockBlobSidecars	missing at admission

Checks 1–2 still need Arc<Parlia<BscChainSpec>> wired into MevApiImpl and remain deferred. Checks 3–4 have no Parlia dependency and are added here.

Also adds the empty-txs guard from Miner.SendBidBlock (before decode).

Changes

• src/rpc/mev.rs: in admit_bid_block, before add_pending_bid_block:
  • empty-txs reject (before decode, mirrors Miner.SendBidBlock line 97)
  • extract_bid_block_deposit_value + gas_fee.is_zero() reject
  • validate_bid_block_blob_sidecars (cheap checks only; KZG at insertion)
• Updated comment to reflect that only the Parlia-dependent checks remain deferred.

Test plan

• cargo clippy --workspace --tests --all-features passes
• cargo test -p reth_bsc -- --test-threads=1 passes
• Builder submitting a BidBlock with no deposit tx now gets an immediate empty gasFee error instead of being silently dropped

🤖 Generated with Claude Code

[hashdit-bot]

Pull Request Review

This PR strengthens mev_sendBidBlock admission checks in a Rust-based blockchain node (reth-bsc, web3 infrastructure) by moving two go-bsc preSealVerifyBidBlock validations earlier into admit_bid_block: gas-fee extraction/zero-fee rejection and blob sidecar invariant validation. It also adds an early guard rejecting empty transaction lists before decode to reduce wasted processing. Overall, the change improves fail-fast behavior and aligns admission flow more closely with go-bsc while leaving Parlia-dependent header/time checks deferred miner-side.

Sensitive Content

No sensitive content detected.

Security Issues

No serious security issues detected.

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