Try harder to create rules backup (#967)

Add a fallback for when a rename does not succeed.

In the case where tempdir is on a different filesystem the
`std::fs::rename` call will fail.

```
This function will return an error in the following situations, but is not limited to just these cases:

  - from does not exist.
  - The user lacks permissions to view contents.
  - from and to are on separate filesystems.
```

https://doc.rust-lang.org/std/fs/fn.rename.html

This commit updates the logic to fallback to a copy and delete.

Closes #965

crates/daemon/src/profiler.rs

@@ -70,7 +70,12 @@ impl Profiler {
                 // create a temp file as the backup location
                 let backup = NamedTempFile::new()?;
                 // move original compiled to backup location
-                fs::rename(&compiled, &backup)?;
+                fs::rename(&compiled, &backup).or_else(|x| {
+                    log::debug!("rename fallback copy");
+                    fs::copy(&compiled, &backup)
+                        .and_then(|_| fs::remove_file(&compiled))
+                        .or(Err(x))
+                })?;
                 // write compiled rules for the profiling run
                 write::compiled_rules(db, &compiled)?;
                 log::debug!("rules backed up to {:?}", backup.path());