Enable selective cache purging in puffin clean (#589)

## Summary

This PR enables `puffin clean` to accept package names as command line
arguments, and selectively purge entries from the cache tied to the
given package.

Relate to #572.

## Test Plan

Modified all the caching tests to run an additional step to (1) purge
the cache, and (2) re-install the package.

crates/puffin-fs/src/lib.rs

@@ -1,6 +1,8 @@
-use std::path::Path;
+use std::path::{Path, PathBuf};
 
+use fs_err as fs;
 use tempfile::NamedTempFile;
+use tracing::warn;
 
 /// Write `data` to `path` atomically using a temporary file and atomic rename.
 pub async fn write_atomic(path: impl AsRef<Path>, data: impl AsRef<[u8]>) -> std::io::Result<()> {
@@ -43,3 +45,48 @@ pub fn write_atomic_sync(path: impl AsRef<Path>, data: impl AsRef<[u8]>) -> std:
     })?;
     Ok(())
 }
+
+/// Remove the file or directory at `path`, if it exists.
+///
+/// Returns `true` if the file or directory was removed, and `false` if the path did not exist.
+pub fn force_remove_all(path: impl AsRef<Path>) -> Result<bool, std::io::Error> {
+    let path = path.as_ref();
+
+    let metadata = match fs::metadata(path) {
+        Ok(metadata) => metadata,
+        Err(err) if err.kind() == std::io::ErrorKind::NotFound => return Ok(false),
+        Err(err) => return Err(err),
+    };
+
+    if metadata.is_dir() {
+        fs::remove_dir_all(path)?;
+    } else {
+        fs::remove_file(path)?;
+    }
+
+    Ok(true)
+}
+
+/// Iterate over the subdirectories of a directory.
+///
+/// If the directory does not exist, returns an empty iterator.
+pub fn directories(path: impl AsRef<Path>) -> impl Iterator<Item = PathBuf> {
+    path.as_ref()
+        .read_dir()
+        .ok()
+        .into_iter()
+        .flatten()
+        .filter_map(|entry| match entry {
+            Ok(entry) => Some(entry),
+            Err(err) => {
+                warn!("Failed to read entry: {}", err);
+                None
+            }
+        })
+        .filter(|entry| {
+            entry
+                .file_type()
+                .map_or(false, |file_type| file_type.is_dir())
+        })
+        .map(|entry| entry.path())
+}