Properly derive string representation for Ethereum typed txs when tx is not signed

[2dvorak]

Proposed changes

• Currently, tx.String() returns error message if tx is not signed (Eth typed txs only)
  • The following code prints out tx: %!v(PANIC=String method: runtime error: invalid memory address or nil pointer dereference)

    fmt.Printf("tx: %v\n", NewTx(&TxInternalDataEthereumDynamicFee{Amount: big.NewInt(0)}))
    

  • This is because it cannot derive from address using recovery ID (which is empty).
• Add check for nil recovery ID, and fill from with proper string replacement
  • For example, TxInternalDataLegacy replace from with "[invalid sender: nil V field]"

Types of changes

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• Bugfix
• New feature or enhancement
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