Move config schema helper out of codex-core package

Keep package-level codex-core checks focused on the library by moving the schema writer binary into its own workspace package and updating the just recipe to call that package directly.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/write-config-schema/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+edition.workspace = true
+license.workspace = true
+name = "codex-write-config-schema"
+version.workspace = true
+
+[lints]
+workspace = true
+
+[dependencies]
+anyhow = { workspace = true }
+clap = { workspace = true, features = ["derive"] }
+codex-core = { workspace = true }