Replace Python build script with Rust code

.github/workflows/build.yml

@@ -25,5 +25,5 @@ jobs:
 
  - name: check upstream
  run: |
- python3 build.py > newlib.rs
+ cargo run --example generate > newlib.rs
  diff -u src/lib.rs newlib.rs

Cargo.toml

@@ -9,4 +9,9 @@ homepage = "https://github.com/rustls/webpki-roots"
 repository = "https://github.com/rustls/webpki-roots"
 
 [dev-dependencies]
+percent-encoding = "2.3"
+reqwest = { version = "0.11", features = ["rustls-tls-native-roots"] }
+ring = "0.16.20"
+rustls-pemfile = "1"
+tokio = { version = "1", features = ["macros", "rt-multi-thread"] }
 webpki = { package = "rustls-webpki", version = "0.101.0" }