Increase test coverage for `IsReattachableCommand`

[lzpap]

The command itself doesn't have tests for the logic it implements.

Would be great to have some tests for IsReattachableCommandTestCase in is_reattachable_test.py.

Tests should cover:

• An input transaction is found for the address, and it is confirmed.
• An input transaction is found for the address, and it is not confirmed.
• No transaction found for the address.
• Transaction(s) found, but none of them are value transfers.
• More transactions found, only the one with the latest attachement_timestamp is used.