v2.65.0: Structurizer: ISA-neutral dominator-based structured control-flow pass.

Structurizer: ISA-neutral dominator-based structured control-flow pass.

New module: ablation/analyzers/structurizer.py.

3 things that were not possible before in Ablation:

1. No structured output for any ISA. Every CFG-backed lifter produced
   goto-based IR. Structural reconstruction (if/while/for) was absent.
2. No post-dominator tree. Post-dominators are needed to find the "join"
   point after an if/else diamond. PostDomTree fills this gap.
3. No ISA-neutral decompiler pass. The structurizer works on any CFG that
   exposes .blocks, .entry, .flow, .flow_r() — the same interface as
   dataflow_engine.CFG. Any ISA CFG module can plug in.

New:

• Structurizer(cfg): builds dominator tree + loop info + post-dominator tree,
  then walks RPO to emit WhileNode, IfNode, SequenceNode, ReturnNode,
  BreakNode, ContinueNode.
• Structurizer.structure() -> StructuredNode: returns the tree.
• Structurizer.emit(insn_emitter, func_name) -> str: renders to pseudo-C.
• PostDomTree(cfg): immediate post-dominator tree via reversed-CFG DomTree.
  Used to find if/else join points.
• All node types exported: SequenceNode, InsnNode, IfNode, WhileNode,
  BreakNode, ContinueNode, ReturnNode.
• Docs: docs/module-reference/structurizer.md.

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