fix(files): Writing new files works across devices

`persist` of `tempfile` does not work across
device boundaries, so if the device backing the
temporary directory is e.g. `tmpfs`, then
`persist` fails. It actually had no useful
benefit, so we can just remove it and write to the
destination directly.

Reproduced bug and confirmed fix on a Debian
machine with:

```console
$ sudo mkdir -p /path/to/temp_dir
$ sudo mount -t tmpfs -o size=100m tmpfs /path/to/temp_dir
$ sudo mount | rg 'temp'
tmpfs on /path/to/temp_dir type tmpfs (rw,relatime,size=102400k,inode64)
$ export TMPDIR=/path/to/temp_dir
$ cargo run -- --python class a whatever
```

`TMPDIR` env var is respected by `tempfile`. The
above `cargo run` fails without this patch. (There
is an end-to-end test for file writing, but that
has never failed for some reason... seems like
none of my machines (including Ubuntu 24) or CI
exhibited the issue).

Closes #145

src/main.rs

@@ -4,7 +4,7 @@
 //! deals with CLI argument handling, I/O, threading, and more.
 
 use std::error::Error;
-use std::fs::File;
+use std::fs::{self, File};
 use std::io::{self, stdout, Read, Write};
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
@@ -535,17 +535,11 @@ fn process_path(
         }
 
         if changed {
-            writeln!(stdout, "{}", path.display())?;
-
             debug!("Got new file contents, writing to file: {:?}", path);
-            let mut file = tempfile::Builder::new()
-                .prefix(env!("CARGO_PKG_NAME"))
-                .tempfile()?;
-            trace!("Writing to temporary file: {:?}", file.path());
-            file.write_all(new_contents.as_bytes())?;
-
-            // Atomically replace so SIGINT etc. do not leave dangling crap.
-            file.persist(&path)?;
+            fs::write(&path, new_contents.as_bytes())?;
+
+            // Confirm after successful write.
+            writeln!(stdout, "{}", path.display())?;
         } else {
             debug!(
                 "Skipping writing file anew (nothing changed): {}",
@@ -759,12 +753,6 @@ impl From<ApplicationError> for PathProcessingError {
     }
 }
 
-impl From<tempfile::PersistError> for PathProcessingError {
-    fn from(err: tempfile::PersistError) -> Self {
-        Self::IoError(err.error, Some(err.file.path().to_owned()))
-    }
-}
-
 impl Error for PathProcessingError {}
 
 #[derive(Debug)]