Describe the bug
signTransaction in the contract client / AssembledTransaction is typed according to an old version of Freighter. If you try to pass a modern implementation's signTransaction in, you get type errors.

What version are you on?

    "@stellar/freighter-api": "^3.0.0",
    "@stellar/stellar-sdk": "12.3.0"

To Reproduce
Steps to reproduce the behavior:

1. Create a project using the indicated versions of Freighter and stellar-sdk
2. Initialize a Contract Client or an AssembledTransaction using the signTransaction from Freighter
3. 💥

Expected behavior
It should work with either version of signTransaction. The return value has changed, as shown in the pasted error message above.

It should also work with the other latest SEP-43 interfaces.

We should probably have tests that a Contract Client / AssembledTransaction can be instantiated with both Freighter's methods and the equivalents from Stellar Wallets Kit.

Additional context