rebuild draw()'s traversal to follow forward() execution order, not declaration order

[kingazm]

Description

As per #2

New examples/005.py demonstrates it even clearer, with the order of declaration being different from the one in forward()

Acceptance criteria

• parser.parse() orders LayeredGraph columns by actual module-call order during that pass, not named_children() order.
• Declared-but-unused layers (e.g. fc4/fc5 in SimpleMLP) no longer appear in the rendered graph.
• Untraceable models fail with a clear error instead of silently reverting to declaration order.
• Add coverage for reordered-declaration, unused-layer-exclusion, and repeated-call cases.