Avoid deadlocks when multiple uv processes lock resources (#6790)

This is achieved by updating the `LockedFile::acquire` API to be async —
as in some cases we were attempting to acquire the lock synchronously,
i.e., without yielding, which blocked the runtime.

Closes https://github.com/astral-sh/uv/issues/6691 — I tested with the
reproduction there and a local release build and no longer reproduce the
deadlock with these changes.

Some additional context in the [internal Discord
thread](https://discord.com/channels/1039017663004942429/1278430431204741270/1278478941262188595)

crates/uv-python/src/installation.rs

@@ -124,7 +124,7 @@ impl PythonInstallation {
         let installations = ManagedPythonInstallations::from_settings()?.init()?;
         let installations_dir = installations.root();
         let cache_dir = installations.cache();
-        let _lock = installations.acquire_lock()?;
+        let _lock = installations.lock().await?;
 
         let download = ManagedPythonDownload::from_request(&request)?;
         let client = client_builder.build();