fix: support arm64 build for Linux (#1225)

Users were running into issues with glibc mismatches on arm64 linux. In
the past, we did not provide a musl build for arm64 Linux because we had
trouble getting the openssl dependency to build correctly. Though today
I just tried the same trick in `Cargo.toml` that we were doing for
`x86_64-unknown-linux-musl` (using `openssl-sys` with `features =
["vendored"]`), so I'm not sure what problem we had in the past the
builds "just worked" today!

Though one tweak that did have to be made is that the integration tests
for Seccomp/Landlock empirically require longer timeouts on arm64 linux,
or at least on the `ubuntu-24.04-arm` GitHub Runner. As such, we change
the timeouts for arm64 in `codex-rs/linux-sandbox/tests/landlock.rs`.

Though in solving this problem, I decided I needed a turnkey solution
for testing the Linux build(s) from my Mac laptop, so this PR introduces
`.devcontainer/Dockerfile` and `.devcontainer/devcontainer.json` to
facilitate this. Detailed instructions are in `.devcontainer/README.md`.

We will update `dotslash-config.json` and other release-related scripts
in a follow-up PR.

.github/workflows/rust-release.yml

@@ -69,6 +69,8 @@ jobs:
             target: x86_64-unknown-linux-musl
           - runner: ubuntu-24.04
             target: x86_64-unknown-linux-gnu
+          - runner: ubuntu-24.04-arm
+            target: aarch64-unknown-linux-musl
           - runner: ubuntu-24.04-arm
             target: aarch64-unknown-linux-gnu
 
@@ -88,7 +90,7 @@ jobs:
             ${{ github.workspace }}/codex-rs/target/
           key: cargo-release-${{ matrix.runner }}-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}
 
-      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' }}
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
         name: Install musl build tools
         run: |
           sudo apt install -y musl-tools pkg-config