fix: Resolve compilation errors in parallel and cache modules

- Fix parallel execution logic to properly handle JoinHandle<Result<R, E>> types
- Use join_all instead of try_join_all for proper Result handling
- Fix double question mark (??) issue in parallel execution methods
- Clean up unused imports in parallel and cache modules
- Ensure all performance optimization modules compile successfully
- Fix CI build failures caused by compilation errors

debian/apt-ostreed/DEBIAN/postrm

@@ -0,0 +1,86 @@
+#!/bin/sh
+set -e
+
+# Source debconf library
+. /usr/share/debconf/confmodule
+
+# Define package name
+PACKAGE="apt-ostreed"
+
+# Function to log messages
+log() {
+    echo "$PACKAGE: $1" >&2
+}
+
+# Function to check if systemd is available
+check_systemd() {
+    if ! command -v systemctl >/dev/null 2>&1; then
+        return 1
+    fi
+    return 0
+}
+
+# Function to stop and disable the service
+cleanup_service() {
+    if ! check_systemd; then
+        return 0
+    fi
+
+    log "Cleaning up apt-ostreed service..."
+
+    # Stop the service if running
+    if systemctl is-active --quiet apt-ostreed.service; then
+        if systemctl stop apt-ostreed.service; then
+            log "apt-ostreed service stopped"
+        else
+            log "Warning: Failed to stop apt-ostreed service"
+        fi
+    fi
+
+    # Disable the service
+    if systemctl is-enabled --quiet apt-ostreed.service; then
+        if systemctl disable apt-ostreed.service; then
+            log "apt-ostreed service disabled"
+        else
+            log "Warning: Failed to disable apt-ostreed service"
+        fi
+    fi
+
+    # Reload systemd daemon
+    systemctl daemon-reload
+}
+
+# Function to cleanup directories (only on purge)
+cleanup_directories() {
+    if [ "$1" = "purge" ]; then
+        log "Purging apt-ostreed directories..."
+        
+        # Remove log files (but keep directory structure)
+        rm -f /var/log/apt-ostreed/*
+        
+        # Remove cache files (but keep directory structure)
+        rm -rf /var/cache/apt-ostree/*
+        
+        # Remove state files (but keep directory structure)
+        rm -rf /var/lib/apt-ostree/*
+        
+        log "Directory cleanup completed"
+    fi
+}
+
+# Main execution
+case "$1" in
+    remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
+        cleanup_service
+        ;;
+    purge)
+        cleanup_service
+        cleanup_directories "$1"
+        ;;
+    *)
+        log "Unknown action: $1"
+        exit 1
+        ;;
+esac
+
+exit 0