feat!: use OZ FT contract

[chadoh]

Fixes #39

Requires upstream Stellar CLI changes:

• Remove contract alias length limit stellar/stellar-cli#2028
• fix(ts-bindings): valid TS when >1 contracterror stellar/stellar-cli#2031

[willemneal]

Suggested change

	let owner: Address = e.storage().instance().get(&OWNER).expect("owner should be set");
	if owner != caller {
	panic_with_error!(e, ExampleContractError::Unauthorized);
	}
	pausable::pause(e, &caller);
	}
	fn unpause(e: &Env, caller: Address) {
	// When `ownable` module is available,
	// the following checks should be equivalent to:
	// `ownable::only_owner(&e);`
	let owner: Address = e.storage().instance().get(&OWNER).expect("owner should be set");
	let owner: Address = e.storage().instance().get(&OWNER).unwrap_optimized();
	if owner != caller {
	panic_with_error!(e, ExampleContractError::Unauthorized);
	}
	pausable::pause(e, &caller);
	}
	fn unpause(e: &Env, caller: Address) {
	// When `ownable` module is available,
	// the following checks should be equivalent to:
	// `ownable::only_owner(&e);`
	let owner: Address = e.storage().instance().get(&OWNER)..unwrap_optimized();

Since the contract can't be deployed with setting the owner it's probably better to use this version of unwrap as it's provided by the soroban-sdk and is well, optimized.

I'm also confused why we need to pass the caller. Couldn't we just do owner.require_auth()? It seems like an extra unneeded check here.

This is something not worth slowing things down here but I think that it is probably because the authors assumed you needed to pass the account.

The CLI currently has a bug for auth where it only considers accounts that were passed in rather than any account referenced in the auth entries provided by simulation. So perhaps they were using the CLI and found that they needed to pass the account to have auth work correctly.

I'll open an issue there about it and with OZ.

[chadoh]

This contract is copied directly over from their examples. Can you send them a PR or some comments upstream?