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_caption_size.py

@@ -1,87 +0,0 @@
-#!/usr/bin/env python3
-"""Test Caption size/w/h properties"""
-import sys
-import mcrfpy
-
-print("Testing Caption size/w/h properties...")
-
-font = mcrfpy.Font("assets/JetbrainsMono.ttf")
-caption = mcrfpy.Caption(text="Test Caption", pos=(100, 100), font=font)
-print(f"Caption created: {caption}")
-
-# Test size property
-print("Testing size property...")
-size = caption.size
-print(f"size type: {type(size)}")
-print(f"size value: {size}")
-
-if not hasattr(size, 'x'):
-    print(f"FAIL: size should be Vector, got {type(size)}")
-    sys.exit(1)
-
-print(f"size.x={size.x}, size.y={size.y}")
-
-if size.x <= 0 or size.y <= 0:
-    print(f"FAIL: size should be positive, got ({size.x}, {size.y})")
-    sys.exit(1)
-
-# Test w property
-print("Testing w property...")
-w = caption.w
-print(f"w type: {type(w)}, value: {w}")
-
-if not isinstance(w, float):
-    print(f"FAIL: w should be float, got {type(w)}")
-    sys.exit(1)
-
-if w <= 0:
-    print(f"FAIL: w should be positive, got {w}")
-    sys.exit(1)
-
-# Test h property
-print("Testing h property...")
-h = caption.h
-print(f"h type: {type(h)}, value: {h}")
-
-if not isinstance(h, float):
-    print(f"FAIL: h should be float, got {type(h)}")
-    sys.exit(1)
-
-if h <= 0:
-    print(f"FAIL: h should be positive, got {h}")
-    sys.exit(1)
-
-# Verify w and h match size
-if abs(w - size.x) >= 0.001:
-    print(f"FAIL: w ({w}) should match size.x ({size.x})")
-    sys.exit(1)
-
-if abs(h - size.y) >= 0.001:
-    print(f"FAIL: h ({h}) should match size.y ({size.y})")
-    sys.exit(1)
-
-# Verify read-only
-print("Checking that size/w/h are read-only...")
-try:
-    caption.size = mcrfpy.Vector(100, 100)
-    print("FAIL: size should be read-only")
-    sys.exit(1)
-except AttributeError:
-    print("  size is correctly read-only")
-
-try:
-    caption.w = 100
-    print("FAIL: w should be read-only")
-    sys.exit(1)
-except AttributeError:
-    print("  w is correctly read-only")
-
-try:
-    caption.h = 100
-    print("FAIL: h should be read-only")
-    sys.exit(1)
-except AttributeError:
-    print("  h is correctly read-only")
-
-print("PASS: Caption size/w/h properties work correctly!")
-sys.exit(0)