feat: redesign sandbox config (#1373)

This is a major redesign of how sandbox configuration works and aims to
fix https://github.com/openai/codex/issues/1248. Specifically, it
replaces `sandbox_permissions` in `config.toml` (and the
`-s`/`--sandbox-permission` CLI flags) with a "table" with effectively
three variants:

```toml
# Safest option: full disk is read-only, but writes and network access are disallowed.
[sandbox]
mode = "read-only"

# The cwd of the Codex task is writable, as well as $TMPDIR on macOS.
# writable_roots can be used to specify additional writable folders.
[sandbox]
mode = "workspace-write"
writable_roots = []  # Optional, defaults to the empty list.
network_access = false  # Optional, defaults to false.

# Disable sandboxing: use at your own risk!!!
[sandbox]
mode = "danger-full-access"
```

This should make sandboxing easier to reason about. While we have
dropped support for `-s`, the way it works now is:

- no flags => `read-only`
- `--full-auto` => `workspace-write`
- currently, there is no way to specify `danger-full-access` via a CLI
flag, but we will revisit that as part of
https://github.com/openai/codex/issues/1254

Outstanding issue:

- As noted in the `TODO` on `SandboxPolicy::is_unrestricted()`, we are
still conflating sandbox preferences with approval preferences in that
case, which needs to be cleaned up.

codex-rs/linux-sandbox/Cargo.toml

@@ -15,15 +15,9 @@ path = "src/lib.rs"
 workspace = true
 
 [dependencies]
+anyhow = "1"
 clap = { version = "4", features = ["derive"] }
 codex-core = { path = "../core" }
-codex-common = { path = "../common", features = ["cli"] }
-
-# Used for error handling in the helper that unifies runtime dispatch across
-# binaries.
-anyhow = "1"
-# Required to construct a Tokio runtime for async execution of the caller's
-# entry-point.
 tokio = { version = "1", features = ["rt-multi-thread"] }
 
 [dev-dependencies]