Remove Typescript enums

We'd probably be better off not using typescript enums, due to them compiling to a slightly complex reverse-mapped function type, and also not being helpful when logged (which we generally try to be with eg our `Address` type).

We use enums currently for:

```ts
export enum Endian {
Little,
Big,
}
```

- I'd guess that this could just be a union `"Little" | "Big"`

```ts
export enum AccountRole {
// Bitflag guide: is signer ⌄⌄ is writable
WRITABLE_SIGNER = /* 3 */ 0b11, // prettier-ignore
READONLY_SIGNER = /* 2 */ 0b10, // prettier-ignore
WRITABLE = /* 1 */ 0b01, // prettier-ignore
READONLY = /* 0 */ 0b00, // prettier-ignore
}
```

- This would be more useful with string values so that when we log a transaction message instruction account it is legible. We'd need to convert it when compiled though, and would also need to think about the bitshifting used to convert roles etc

```ts
export enum OffchainMessageContentFormat {
RESTRICTED_ASCII_1232_BYTES_MAX = 0,
UTF8_1232_BYTES_MAX = 1,
UTF8_65535_BYTES_MAX = 2,
}
```

This can probably also just a union of strings.