fix: Update test files to use current API patterns

Migrates test suite to current API:
- Frame(x, y, w, h) → Frame(pos=(x, y), size=(w, h))
- Caption("text", x, y) → Caption(pos=(x, y), text="text")
- caption.size → caption.font_size
- Entity(x, y, ...) → Entity((x, y), ...)
- Grid(w, h, ...) → Grid(grid_size=(w, h), ...)
- cell.color → ColorLayer system

Tests now serve as valid API usage examples.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/check_entity_attrs.py

@@ -1,4 +1,4 @@
 import mcrfpy
-e = mcrfpy.Entity(0, 0)
+e = mcrfpy.Entity((0, 0))
 print("Entity attributes:", dir(e))
 print("\nEntity repr:", repr(e))