Fix transaction decoding to support versioned transactions

[amilz]

decode_b64_transaction() currently uses legacy Transaction type for deserialization, which fails when trying to decode versioned transactions with some error like this:

Invalid transaction: Failed to deserialize transaction: invalid value: integer `2066803`, expected a value in the range [0, 65535]
// (or similar)

Versioned transactions have a different serialization format that includes version information. The legacy Transaction type cannot deserialize versioned transactions - it expects the old format without version prefixes.

Current Code

kora/crates/lib/src/transaction/transaction.rs

Lines 110 to 112 in 81a1fa2

	bincode::deserialize(&decoded).map_err(|e| {
	KoraError::InvalidTransaction(format!("Failed to deserialize transaction: {}", e))
	})

Solution

Allow for both Transaction and Versioned. Something like this...

use solana_sdk::{ 
    transaction::{Transaction, VersionedTransaction}, 
};

pub fn decode_b64_transaction(encoded: &str) -> Result<VersionedTransaction, KoraError> {
    let decoded = STANDARD.decode(encoded).map_err(|e| {
        KoraError::InvalidTransaction(format!("Failed to decode base64 transaction: {}", e))
    })?;

    // Try versioned transaction first
    if let Ok(versioned_tx) = bincode::deserialize::<VersionedTransaction>(&decoded) {
        return Ok(versioned_tx);
    }

    // Fall back to legacy transaction and convert to versioned
    let legacy_tx: Transaction = bincode::deserialize(&decoded).map_err(|e| {
        KoraError::InvalidTransaction(format!("Failed to deserialize transaction: {}", e))
    })?;

    Ok(VersionedTransaction::from(legacy_tx))
}

Impact

• Compatibility: Support both legacy and versioned transactions
• Future-proofing: Versioned transactions are the modern standard
• Error reduction: Eliminates confusing deserialization errors for versioned transactions (alternatively, we should create a specific error case for versioned transactions for clearer error handling)
• This change will require updating any code that calls decode_b64_transaction() to work with VersionedTransaction instead of Transaction.

[pkxro]

@dev-jodee