A function to fetch a decompiled `Transaction` by signature

## Motivation

If you want to fetch a transaction from the RPC by signature today you might do something like this:

```ts
const result = await rpc
.getTransaction(
signature(
"265Vry9E7VMD92AX79R1A5zaBmyYAMVarZq4YTWCrCnhzBtEAFaHYrbWHmdi5wvJoWGdeH9jKvAgMLVncQUBGEK1"
),
{ encoding: "base64" }
)
.send();

if (!result) {
throw Error("Transaction not found");
}

const {
transaction: [wireTransaction],
} = result;

const transferCheckedInstruction = pipe(
wireTransaction,

// Decode the wire transaction.
getBase64Encoder().encode,
getTransactionDecoder().decode,

// Decode the message.
(transaction) =>
getCompiledTransactionMessageDecoder().decode(transaction.messageBytes),
decompileTransactionMessage
);
```

That's probably enough boilerplate to extract into a helper.

## Example use case

```ts
const transaction = await fetchDecompiledTransaction(
rpc,
signature('265Vry9E7VMD92AX79R1A5zaBmyYAMVarZq4YTWCrCnhzBtEAFaHYrbWHmdi5wvJoWGdeH9jKvAgMLVncQUBGEK1'),
);

for (const instruction in transaction.instructions) {
// ...
}
```

## Details

Implement this in `@solana/transactions` as `fetchDecompiledTransaction(rpc: Rpc, signature: Signature)`.