Remove separate test files in favor of same-file mod tests (#9199)

## Summary

These were moved as part of a broader refactor to create a single
integration test module. That "single integration test module" did
indeed have a big impact on compile times, which is great! But we aren't
seeing any benefit from moving these tests into their own files (despite
the claim in [this blog
post](https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html),
I see the same compilation pattern regardless of where the tests are
located). Plus, we don't have many of these, and same-file tests is such
a strong Rust convention.

crates/uv-dev/src/generate_options_reference.rs

@@ -386,4 +386,24 @@ impl Visit for CollectOptionsVisitor {
 }
 
 #[cfg(test)]
-mod tests;
+mod tests {
+    use std::env;
+
+    use anyhow::Result;
+
+    use uv_static::EnvVars;
+
+    use crate::generate_all::Mode;
+
+    use super::{main, Args};
+
+    #[test]
+    fn test_generate_options_reference() -> Result<()> {
+        let mode = if env::var(EnvVars::UV_UPDATE_SCHEMA).as_deref() == Ok("1") {
+            Mode::Write
+        } else {
+            Mode::Check
+        };
+        main(&Args { mode })
+    }
+}