Allow validated credit creation transactions

[webbananaunite]

Summary

• Treat transactions whose withdrawal account is the money-supply account (-) as credit creation and skip the normal maker balance check for them.
• Restrict credit creation validation to allowed issuance claims: booker fee, basic income, and born.
• Build block booker-fee transactions as balanced credit-creation transactions with the booker as the deposit account.
• Add regression tests for booker-fee credit creation and ordinary no-balance transactions.

Verification

• swift test --build-path /Users/yoichi/appOutput/blocks
• /Users/yoichi/.swiftly/bin/swift build -v --swift-sdk x86_64-swift-linux-musl --build-path /Users/yoichi/appOutput/blocks-linux-musl