stress-test: add sequential upload, bulk bitswap read, and renew scenarios

[karolk91]

Description

Adds three new stress test scenarios to the bulletin-stress-test crate, along with supporting infrastructure.

New scenarios

Sequential nonce upload (throughput sequential-upload)
Single-account upload using sequential nonces with per-block re-signing. Uses system_accountNextIndex for best-block nonce tracking and create_partial_offline for zero-RPC signing. Supports --total-size, --chunk-size, and --instances for parallel uploads.

Bulk bitswap read (bitswap bulk-read)
Discovers CIDs from on-chain TransactionStorage::Transactions via SCALE decoding, then downloads them round-robin with configurable concurrency and multi-peer support. Supports --read-size, --read-concurrency, --min-size, --max-size, --batch-size.

Renew stress (renew)
Uploads items then fills blocks with renew extrinsics, logging System::BlockWeight per block for weight verification. Supports --store-count, --chunk-size, --target-blocks.

Bitswap client improvements

• Multi-CID batched wantlists (up to 16 CIDs per request)
• VecDeque-based response matching to fix stale substream race condition
• Codec limit increased from 2 MB to 16 MB
• Multi-peer round-robin worker distribution

CLI improvements

• Multi-RPC submission via comma-separated --ws-url
• Multi-peer bitswap via comma-separated --p2p-multiaddr
• P2P address auto-discovery via system_networkState RPC
• tracing output directed to stderr (stdout reserved for --output json)

Zombienet integration tests

• test_parachain_bitswap_read — B2 concurrent read sweep (1–64 clients)
• test_parachain_bitswap_bulk_read — upload 100 MB mixed, read 1 GB via bitswap
• test_parachain_sequential_upload — single-account sequential nonce upload
• test_parachain_renew_stress — store 520 items, renew for 5 blocks
• Multi-node network config: 3-core elastic scaling, 2 collators with --ipfs-server, 2 RPC nodes
• assign_cores utility bin for on-chain coretime assignment