feat: implement structured pattern matching with nested constructor support

[metalurgical]

Introduce a full pattern matching pipeline for match expressions, including typed pattern representation, validation, and a structured decision tree.

This establishes a foundation for deterministic and type-safe match evaluation, enabling correct handling of nested patterns and complex destructuring.

Additionally extract tests for parse to new file to reduce file bloat and improve maintainability.

Overview Diagram

flowchart TD
    A["match syntax"] --> B{"Old vs New"}

    B -->|Old| C["2 arms only → normalize"]
    B -->|New| D["multiple arms → analyze → validate → compile"]

    C --> E["Match.left/right"]
    D --> E

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Expanded Diagram

flowchart TD
    A["match syntax"] --> B{"Old vs New"}

    B -->|Old| C1["exactly 2 arms required"]
    C1 --> C2["classify arm pair"]
    C2 --> C3["Left/Right or None/Some or False/True"]
    C3 --> E["Match.left/right"]

    B -->|New| D1["parse multiple arms"]
    D1 --> D2["convert to structured pattern representation"]
    D2 --> D3["assign types to patterns"]

    D3 --> D4["ensure all arms use the same match kind"]
    D4 --> D5["check for duplicate arms"]
    D5 --> D6["check for overlapping patterns"]
    D6 --> D7["check for unreachable arms"]
    D7 --> D8["check exhaustiveness"]

    D8 --> D9["build decision tree"]
    D9 --> D10["convert back to two-arm form"]
    D10 --> E["Match.left/right"]

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[metalurgical]

Resolves #250
Closes #250