fix: Client is_signer usage in to_account_metas

[Arrowana]

Problem: Not using is_signer prevents proper functioning of the client whenever a PDA is used, let's say when composing and instruction with the inner CPI using the inner client

That is not exactly for the general case but the sole purpose of this argument is for this objective so it seems reasonable to make it work.

From the trait

anchor/lang/src/lib.rs

Lines 154 to 160 in 340e9c1

	pub trait ToAccountMetas {
	/// `is_signer` is given as an optional override for the signer meta field.
	/// This covers the edge case when a program-derived-address needs to relay
	/// a transaction from a client to another program but sign the transaction
	/// before the relay. The client cannot mark the field as a signer, and so
	/// we have to override the is_signer meta field given by the client.
	fn to_account_metas(&self, is_signer: Option<bool>) -> Vec<AccountMeta>;

[vercel]

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

A member of the Team first needs to authorize it.

[acheroncrypto]

Thanks. This seems to be only about composite accounts, correct?

It would also be great to have a CPI test for the problematic scenario this PR solves.

[Arrowana]

Not only about composite, all accounts. It also changes the branch for non composite.

Yes, I can add a test.

[Arrowana]

Thanks. This seems to be only about composite accounts, correct?

It would also be great to have a CPI test for the problematic scenario this PR solves.

I added a test, it is a bit awkward but I believe it implements what is explained in the doc