Add early Django configuration

[SmileyChris]

Summary

This PR implements early Django configuration, addressing several long-standing issues around import order and PEP8 compliance (#34, #43, #85).

The Problem

Previously, Django wasn't configured until app = Django() was called. This meant:

• Django imports that required configuration (like from django.contrib.auth.models import User) had to come after app = Django()
• This violated PEP8 import ordering conventions
• Users had to use defer to work around import order issues
• IDE type checkers (mypy, pyright) struggled with the deferred imports

The Solution

Django is now configured during from nanodjango import Django via a two-phase approach:

Phase 1: Early extraction (AST parsing)

• When you from nanodjango import Django, the source file is parsed via AST
• Simple module-level settings are extracted and evaluated
• Django is configured with these settings, allowing subsequent imports to work

Phase 2: Late update (at Django() instantiation)

• When app = Django() is called, the module has fully executed
• Complex settings (conditionals, function calls) are grabbed from the module namespace
• Django settings are updated with any values that couldn't be extracted earlier

What This Enables

# PEP8-compliant import order now works!
from nanodjango import Django  # isort: skip
from django.db import models
from django.contrib.auth.models import User

# Module-level settings
DEBUG = False
SECRET_KEY = os.environ["SECRET_KEY"]

# Complex/conditional settings work too
if os.environ.get("PRODUCTION"):
    ALLOWED_HOSTS = ["example.com"]
else:
    ALLOWED_HOSTS = ["*"]

app = Django()

class MyModel(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)

Key Implementation Details

1. Lazy loading via __getattr__ (__init__.py)

   • The Django class is only imported when first accessed
   • This ensures early config runs when the user's script imports Django, not when nanodjango is first loaded (important for CLI mode)

2. New early.py module

   • EarlyConfigurator class handles AST parsing and Django setup
   • Extracts simple assignments, annotated assignments, and augmented assignments
   • Injects BASE_DIR, Path, and os into the evaluation context

3. CLI mode support (commands.py)

   • Deferred Django import until after user script is loaded
   • Works with both python script.py and nanodjango run script.py

4. Late settings update (app.py)

   • Scans module namespace for uppercase variables
   • Applies any settings that changed or couldn't be extracted earlier

defer is now rarely needed

With early configuration working in all modes, nanodjango.defer is now only needed for unusual third-party packages that perform initialization at import time in ways that conflict with early configuration.

Test plan

• All 80 existing tests pass
• Direct mode (python script.py) works with User import
• CLI mode (nanodjango run script.py) works with User import
• Conditional settings work (tested with PRODUCTION env var)
• Computed settings work (function call results)
• Module-level settings override defaults
• Constructor settings override module-level settings

Documentation

Updated:

• docs/settings.rst - New module-level settings section with "How it works" explanation
• docs/defer.rst - Note that defer is rarely needed now
• docs/tutorial.rst - Updated model definition guidance
• docs/troubleshooting.rst - Updated "Settings not configured" section
• docs/changelog.rst - Added 0.14.0 entry

Closes #34, #43, #85