Clear backpack.#publicKey on disconnect

[mcintyre94]

This fixes a bug where the connect function is not called properly on a reconnect, as #publicKey is already defined

Specifically this is because of this condition in the wallet-standard wrapper (https://github.com/coral-xyz/backpack/blob/master/packages/wallet-standard/src/wallet.ts#L149):

    #connect: ConnectMethod = async ({ silent } = {}) => {
        if (!silent && !this.#backpack.publicKey) {
            await this.#backpack.connect();
        }

        this.#connected();

        return { accounts: this.accounts };
    };

On the first connect, this.#backpack.publicKey is undefined and this.#backpack.connect() is called correctly

However, on the second connect this.#backpack.publicKey was already set and so this.#backpack.connect() was not called. this.#connected() was called, and since this uses this.#backpack.publicKey it was able to emit an event that made it look to the wallet adapter UI like a connection was successfully performed. But the internal code in this.#backpack.connect() hadn't been called, and so signing didn't actually work.

The fix is to set backpack.#publicKey to undefined on disconnect, so that this.#backpack.connect() is called correctly on the reconnect.

Closes #3555

[vercel]

@mcintyre94 is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.

[armaniferrante]

Thank you!