Function invoke_signed 

pub fn invoke_signed<const ACCOUNTS: usize>(
    instruction: &InstructionView<'_, '_, '_, '_>,
    account_views: &[&AccountView; ACCOUNTS],
    signers_seeds: &[Signer<'_, '_>],
) -> ProgramResult

Invoke a signed CPI with full validation.

Validates account count, address identity, signer/writable requirements, and borrow compatibility before calling the runtime.