feat: refactor plugin architecture, enhance linting, CI & tooling

- Major refactor of core Fish functions for modularity, caching, and error handling
- Improved `.editorconfig` and Makefile for stricter formatting and linting standards
- Expanded linting support: added EditorConfig checks, auto-install for missing tools, and Makefile targets
- Enhanced CI workflow with clearer permissions and job steps in GitHub Actions
- Updated documentation in `README.md` and `CLAUDE.md` to reflect new features, advanced developer tools, and contribution guidelines
- Improved Node.js version manager detection, switching, and installation logic
- Added/updated utility functions for configuration, silent mode, notifications, and version extraction
- Various bug fixes, code quality improvements, and expanded test coverage

functions/nvm_cache.fish

@@ -0,0 +1,110 @@
+function nvm_cache -d "XDG-compliant cache management with TTL"
+    set -l action $argv[1]
+    set -l key $argv[2]
+    set -l value $argv[3]
+    set -l ttl $argv[4]
+
+    switch $action
+        case get
+            _nvm_cache_get "$key" "$ttl"
+        case set
+            _nvm_cache_set "$key" "$value"
+        case delete
+            _nvm_cache_delete "$key"
+        case clear
+            _nvm_cache_clear
+        case stats
+            _nvm_cache_stats
+        case '*'
+            echo "Usage: nvm_cache [get|set|delete|clear|stats] <key> [value] [ttl]"
+            return 1
+    end
+end
+
+function _nvm_cache_dir -d "Get XDG cache directory for nvm-auto-use"
+    if set -q XDG_CACHE_HOME
+        echo "$XDG_CACHE_HOME/nvm-auto-use"
+    else
+        echo "$HOME/.cache/nvm-auto-use"
+    end
+end
+
+function _nvm_cache_get -d "Get cache value by key, respecting TTL"
+    set -l key $argv[1]
+    set -l ttl $argv[2]
+    set -l cache_dir (_nvm_cache_dir)
+    set -l cache_file "$cache_dir/$key"
+
+    if not test -f "$cache_file"
+        return 1
+    end
+
+    # Check TTL
+    set -l cache_time (stat -c %Y "$cache_file" 2>/dev/null; or stat -f %m "$cache_file" 2>/dev/null)
+    set -l current_time (date +%s)
+    set -l default_ttl 300 # 5 minutes default
+
+    if test -n "$ttl"
+        set default_ttl $ttl
+    end
+
+    if test (math "$current_time - $cache_time") -gt $default_ttl
+        rm "$cache_file" 2>/dev/null
+        return 1
+    end
+
+    cat "$cache_file"
+    return 0
+end
+
+function _nvm_cache_set -d "Set cache value by key"
+    set -l key $argv[1]
+    set -l value $argv[2]
+    set -l cache_dir (_nvm_cache_dir)
+    set -l cache_file "$cache_dir/$key"
+
+    if test -z "$value"
+        return 1
+    end
+
+    mkdir -p "$cache_dir" 2>/dev/null
+    echo "$value" >"$cache_file" 2>/dev/null
+    return $status
+end
+
+function _nvm_cache_delete -d "Delete cache value by key"
+    set -l key $argv[1]
+    set -l cache_dir (_nvm_cache_dir)
+    set -l cache_file "$cache_dir/$key"
+    rm "$cache_file" 2>/dev/null
+    return 0
+end
+
+function _nvm_cache_clear -d "Clear all cache files"
+    set -l cache_dir (_nvm_cache_dir)
+    rm -rf "$cache_dir" 2>/dev/null
+    return 0
+end
+
+function _nvm_cache_stats -d "Show cache statistics"
+    set -l cache_dir (_nvm_cache_dir)
+    if test -d "$cache_dir"
+        echo "Cache directory: $cache_dir"
+        echo "Cache files: "(find "$cache_dir" -type f 2>/dev/null | wc -l)
+        echo "Cache size: "(du -sh "$cache_dir" 2>/dev/null | cut -f1)
+    else
+        echo "No cache directory found"
+    end
+    return 0
+end
+
+function _nvm_cache_key -d "Generate cache key from directory and file"
+    set -l dir (pwd)
+    set -l file_hash (echo "$argv[1]" | shasum | cut -d' ' -f1)
+    echo "dir_$(echo "$dir" | shasum | cut -d' ' -f1)_$file_hash"
+end
+
+function _nvm_cache_manager_key -d "Generate cache key for manager availability"
+    set -l manager $argv[1]
+    echo "manager_$manager"
+end