feat: add --dangerously-bypass-approvals-and-sandbox (#1384)

This PR reworks `assess_command_safety()` so that the combination of
`AskForApproval::Never` and `SandboxPolicy::DangerFullAccess` ensures
that commands are run without _any_ sandbox and the user should never be
prompted. In turn, it adds support for a new
`--dangerously-bypass-approvals-and-sandbox` flag (that cannot be used
with `--approval-policy` or `--full-auto`) that sets both of those
options.

Fixes https://github.com/openai/codex/issues/1254

codex-rs/core/src/protocol.rs

@@ -231,12 +231,6 @@ impl SandboxPolicy {
             }
         }
     }
-
-    // TODO(mbolin): This conflates sandbox policy and approval policy and
-    // should go away.
-    pub fn is_unrestricted(&self) -> bool {
-        matches!(self, SandboxPolicy::DangerFullAccess)
-    }
 }
 
 /// User input