replace rustlings-macros with build script

This turns rustlings into a single crate, which is less complicated to
publish releases for. A follow-up step might be to remove the workspace
configuration.

The motivation was this discussion on Zulip:
https://rust-lang.zulipchat.com/#narrow/channel/334454-t-lang-docs.2Frustlings/topic/Trusted.20publishing/near/638396712

Cargo.toml

@@ -36,10 +36,12 @@ keywords = [
 ]
 include = [
   "/src/",
+  "/build.rs",
   "/exercises/",
   "/solutions/",
   # A symlink to be able to include `dev/Cargo.toml` although `dev` is excluded.
   "/dev-Cargo.toml",
+  "/info.toml",
   "/README.md",
   "/LICENSE",
 ]
@@ -49,7 +51,6 @@ anyhow = "1"
 clap = { version = "4", features = ["derive"] }
 crossterm = { version = "0.29", default-features = false, features = ["windows", "events"] }
 notify = "8"
-rustlings-macros = { path = "rustlings-macros", version = "=6.5.0" }
 serde_json = "1"
 serde.workspace = true
 shlex = "2"
@@ -59,6 +60,11 @@ wait-timeout = "0.2"
 [target.'cfg(not(windows))'.dependencies]
 rustix = { version = "1.0", default-features = false, features = ["std", "stdio", "termios"] }
 
+[build-dependencies]
+quote = "1"
+serde.workspace = true
+toml.workspace = true
+
 [dev-dependencies]
 tempfile = "3"