feat(tron): add tx signing, fee estimation, and withdrawals

[shamardy]

Summary

Add transaction signing, fee estimation, and the full withdraw pipeline for TRX native and TRC20 token transfers. This is the fourth PR in the TRON integration series:

1. feat(tron): initial groundwork for full TRON integration #2425 — Initial groundwork (ChainSpec, TronAddress)
2. feat(tron): add HD wallet activation via EthCoin pipeline #2467 — HD wallet activation via EthCoin pipeline
3. feat(tron): add TRC20 token activation and balance queries #2712 — TRC20 token activation and balance queries
4. This PR — Transaction building, signing, fee estimation, and withdrawals

Key Features

• Local protobuf transaction building using prost::Message derive macros — no dependency on node-side transaction creation
• SHA256 + secp256k1 signing — same curve as EVM but with SHA256 digest (not Keccak256), TAPOS anti-replay (not nonces), and 65-byte r||s||v signatures with v ∈ {0,1}
• Bandwidth + energy fee estimation — bandwidth charged per byte of serialized tx, energy charged per unit of smart contract execution (TRC20); both priced in SUN and converted to TRX at chain rate
• New TxFeeDetails::Tron variant — reports bandwidth_used, energy_used, bandwidth_fee, energy_fee, total_fee in withdraw responses
• Chain-dispatched broadcast via send_raw_tx — TRON protobuf hex routes to /wallet/broadcasthex, EVM RLP routes to eth_sendRawTransaction
• Full withdraw support for both TRX and TRC20 in iguana and HD wallet modes, with max-send fee deduction for TRX and cross-asset fee verification for TRC20

Architecture

New modules under mm2src/coins/eth/tron/:

Module	Purpose
proto.rs	Minimal TRON protobuf types (Transaction, TransactionRaw, TransferContract, TriggerSmartContract) with correct non-sequential field tags
tx_builder.rs	Unsigned transaction builders for TRX transfers and TRC20 transfer(address,uint256) calls, with TAPOS reference block computation
sign.rs	sign_tron_transaction() — SHA256 digest → secp256k1 sign → 65-byte signature with recovery id normalization
fee.rs	Bandwidth estimation from serialized tx size, energy estimation via triggerconstantcontract, fee calculation with resource deficit logic
withdraw.rs	build_tron_trx_withdraw() with iterative max-send convergence, build_tron_trc20_withdraw() with cross-asset TRX balance verification

Modified files:

File	Changes
eth/tron/api.rs	get_account_resource(), broadcast_hex(), extended getnowblock for TAPOS block data
eth/eth_withdraw.rs	TRON signing path replaces stub, TRON-specific fee estimation and memo rejection
eth.rs	send_raw_tx chain dispatch (TRON → broadcast_hex, EVM → eth_sendRawTransaction)
lp_coins.rs / tx_fee_details.rs	TxFeeDetails::Tron variant

Test Coverage

7 withdraw integration tests (cargo test --test mm2_tests_main --features tron-network-tests -- tron):

Test	Coverage
test_trx_withdraw_and_send	TRX withdraw + broadcast on Nile, exact spent_by_me/my_balance_change assertions
test_trc20_withdraw_and_send	TRC20 USDT withdraw + broadcast, verifies fees paid in TRX (not token)
test_trx_withdraw_max	Max TRX withdraw — fee deduction, total_amount + fee ≈ balance
test_trx_withdraw_hd	HD wallet TRX withdraw from derivation index 1
test_trc20_withdraw_hd	HD wallet TRC20 withdraw with energy fee verification
test_trx_withdraw_insufficient_balance	Unfunded HD index 2 rejects with proper error
test_trx_fee_details_structure	All TxFeeDetails::Tron fields present with correct types and values

Coin Configuration (unchanged from #2712)

{
  "coin": "TRX",
  "name": "tron",
  "fname": "TRON",
  "mm2": 1,
  "wallet_only": true,
  "chain_id": 728126428,
  "protocol": { "type": "TRON" }
}

TRON Roadmap (Next Steps)

This PR completes wallet-only TRON support. The following items remain for full TRON parity with EVM chains:

• Atomic swap support — implement HTLC swap operations (SwapOps, MakerCoinSwapOpsV2, TakerCoinSwapOpsV2), order matching integration, and trade fee methods
• Etomic swap contract for TVM — adapt EtomicSwapMakerV2/TakerV2 Solidity contracts for TVM deployment (TVM is EVM-compatible but uses different address format and energy model); deploy to Nile testnet → test → deploy to mainnet
• Release full TRON integration — once swaps and contracts are complete, merge the full stack into dev and cut a release with TRX/TRC20 swap support
• TRX staking (Stake V2) — allow users to stake TRX to acquire bandwidth and energy resources via TRON's Stake 2.0 mechanism (TIP-467), reducing transaction fees; includes staking, unstaking (14-day lock), and resource delegation
• Dockerized TRON node for CI — run a local TRON node in Docker for deterministic integration tests (currently using public Nile testnet nodes which can be flaky)
• Chain abstraction refactor — unify EVM and TRON under common RPC, transaction pipeline, broadcast session, and receipt finality abstractions; eliminate duplicated dispatch logic and move toward a typed chain model where invalid chain×asset combinations are unrepresentable
• Remaining feature parity — WalletConnect signing support (TRON uses ETH protocol for WC, separate coin config), Trezor hardware wallet signing, MetaMask integration, TRON message signing/verification (different format from EVM), NFT support (TRC-721/TRC-1155), transaction history sync

Partially addresses #1542 and #1698.

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