feat: add ChainSimulatorSetTokenBalanceStep for arbitrary ESDT balance creation

[EtienneWallet]

Summary

Add a new chain-simulator-only step ChainSimulatorSetTokenBalanceStep that enables creating arbitrary fungible ESDT token balances "from thin air" on accounts. This is useful for test scenarios where you want to set up specific token balances without needing to clone accounts from a source network.

Key Features

• Fungible tokens only (v1): Supports setting arbitrary amounts for standard ESDT tokens
• Automatic token registration: If a token doesn't exist on the chain simulator, it's automatically cloned from the source network (default: mainnet)
• Multi-receiver support: Set balances for multiple accounts in a single step
• Storage preservation: Uses set_address_state() to surgically update balances without affecting other account state (code, nonce, balance)
• Idempotent behavior: Re-running with the same or different amounts updates balances cleanly

Changes

• ChainSimulatorSetTokenBalanceStep implementation with protobuf encoding for ESDT values
• Helper functions for storage key generation and value encoding
• Support for reusing existing ESDT token reconciliation logic from AccountCloneStep
• 28 unit tests covering encoding, validation, and execution paths
• Integration test demonstrating end-to-end balance creation and verification
• User and developer documentation

Testing

• All 296 unit tests pass (including 28 new tests for this step)
• All code quality gates pass (bandit, flake8, ruff, pylint > 9.5)
• Integration test successfully creates balances on chain simulator and verifies via proxy queries