Organize test suite: add README, move loose tests to proper directories

- Add tests/README.md documenting test structure and usage
- Move issue_*_test.py files to tests/regression/ (9 files)
- Move loose test_*.py files to tests/unit/ (18 files)
- tests/ root now contains only pytest infrastructure

Addresses #166

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_module_namespace.py

@@ -1,61 +0,0 @@
-#!/usr/bin/env python3
-"""Test module namespace changes (#184, #189)"""
-import sys
-import mcrfpy
-
-print("Testing module namespace changes (#184, #189)...")
-
-# Test window singleton exists (#184)
-print("Testing window singleton...")
-if not hasattr(mcrfpy, 'window'):
-    print("FAIL: mcrfpy.window should exist")
-    sys.exit(1)
-
-window = mcrfpy.window
-if window is None:
-    print("FAIL: window should not be None")
-    sys.exit(1)
-
-# Verify window properties
-if not hasattr(window, 'resolution'):
-    print("FAIL: window should have resolution property")
-    sys.exit(1)
-
-print(f"  window exists: {window}")
-print(f"  window.resolution: {window.resolution}")
-
-# Test that internal types are hidden from module namespace (#189)
-print("Testing hidden internal types...")
-hidden_types = ['UICollectionIter', 'UIEntityCollectionIter', 'GridPoint', 'GridPointState']
-visible = []
-for name in hidden_types:
-    if hasattr(mcrfpy, name):
-        visible.append(name)
-
-if visible:
-    print(f"FAIL: These types should be hidden from module namespace: {visible}")
-    # Note: This is a soft fail - if these are expected to be visible, adjust the test
-    # sys.exit(1)
-else:
-    print("  All internal types are hidden from module namespace")
-
-# But iteration should still work - test UICollection iteration
-print("Testing that iteration still works...")
-scene = mcrfpy.Scene("test_scene")
-ui = scene.children
-ui.append(mcrfpy.Frame(pos=(0,0), size=(50,50)))
-ui.append(mcrfpy.Caption(text="hi", pos=(0,0)))
-
-count = 0
-for item in ui:
-    count += 1
-    print(f"  Iterated item: {item}")
-
-if count != 2:
-    print(f"FAIL: Should iterate over 2 items, got {count}")
-    sys.exit(1)
-
-print("  Iteration works correctly")
-
-print("PASS: Module namespace changes work correctly!")
-sys.exit(0)