fix(system): fix system return statement in inner blocks

[notdanilo]

Status	Type	⚠️ Core Change	Issue
Ready	Hotfix	No	None

Problem

We cannot write return Ok(ctx.accounts) in inner blocks of the execute function.

Solution

Fix the #[system] proc-macro to recursively look for return Ok(ctx.accounts) and transform them to return ctx.accounts.try_to_vec().