Allow swapping inscriptions using the offers command

[SatoshiRoppongi]

#4251

Implemented Features

1. Payment Enum Addition:
   - Payment::Amount(Amount) - Bitcoin amount payment (existing functionality)
   - Payment::InscriptionId(InscriptionId) - Inscription ID payment (new functionality)
2. Command Interface Changes:
   - Changed --amount parameter to --for
   - --for accepts either a Bitcoin amount or an inscription ID
3. Create Functionality (src/subcommand/wallet/offer/create.rs):
   - Bitcoin Payment: Maintains existing logic for Bitcoin-based offers
   - Inscription Payment: Validates payment inscription exists in wallet and creates transaction with two inputs (target inscription + payment inscription)
4. Accept Functionality (src/subcommand/wallet/offer/accept.rs):
   - Bitcoin Payment: Validates using balance change verification
   - Inscription Payment: Verifies that the specified inscription is present in the PSBT inputs

Command Examples

Bitcoin payment (existing functionality)

ord wallet offer create --inscription --for 1btc --fee-rate 1
ord wallet offer accept --inscription --for 1btc --psbt

Inscription-to-inscription swap (new functionality)

ord wallet offer create --inscription --for --fee-rate 1
ord wallet offer accept --inscription --for --psbt

Key Technical Details

• Backward Compatibility: Maintains full compatibility with existing Bitcoin-based offers
• Type Safety: Uses Rust's type system with a Payment enum to handle both payment types safely
• Validation: Ensures payment inscriptions exist in wallet before creating offers
• Transaction Structure: Creates proper Bitcoin transactions with multiple inputs for inscription swaps

Testing & Quality Assurance

• Updated all existing tests to use the new --for parameter
• Added comprehensive test for inscription-to-inscription swap functionality
• All tests pass successfully, confirming no regression in existing functionality
• Code passes formatting (just fmt) and linting (just clippy) checks

The implementation enables users to trade inscriptions directly with each other, expanding the utility of the ord wallet beyond Bitcoin-only transactions as originally requested in the GitHub
issue.