fix: Prevent autoload order changing on project startup

[aagrieve]

Problem

Autoloads is reordering on project startup and reload, which causes the project to launch with unsaved changes.

Cause

The plugin adds autoloads unconditionally in _enter_tree() in both netfox.gd and netfox-extras.gd

Solution

Added a check for each autoload before adding when entering the tree. When the autoloads are already configured, no changes are made.

Verification

• Reloaded the project multiple times without autoload order changing
• Restarted the editor multiple times without autoload order changing