Validate transaction size

[manuelmauro]

Summary

• Add transaction size validation to eth_sendTransaction and eth_sendRawTransaction RPC endpoints
• Reject transactions exceeding 128 KiB (matching geth/reth txMaxSize limit)
• Prevents DoS attacks via oversized transactions with large access lists

Changes

• Add encoded_length() and validate_size() methods to TransactionRequest
• Add TX_SLOT_BYTE_SIZE (32 KiB) and DEFAULT_MAX_TX_INPUT_BYTES (128 KiB) constants
• Validate size early in send_transaction before signing
• Validate raw transaction bytes in send_raw_transaction before decoding

References

• reth: https://github.com/paradigmxyz/reth/blob/main/crates/transaction-pool/src/validate/constants.rs#L11

Note

Depends on: moonbeam-foundation/ethereum#2

Uses a temporary patch for the ethereum crate to access encoded_len(). This should be removed once the changes are released.