Source generator for lazy properties and methods

### Overview

Provide a source generator that will make it quicker to define a lazily-instantiable property value. The underlying mechanism may use the provided `System.Lazy` type. The generator may also support the partial properties feature introduced in C# 13.

This will be an alternative option to [Lombok.NET's `Lazy`](https://github.com/CollinAlpert/Lombok.NET?tab=readme-ov-file#lazy) generator. The reason being that Lombok forces an irregular structure, instantiating a class instance to hold the value and refer to its instance holding the globally initialized lazy value. It's also less flexible, not conveniently supporting per-instance lazy instances out of the box.

### API breakdown

```csharp
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Method, Inheritable = false, AllowMultiple = false)]
public class LazyAttribute(string methodName) : Attribute
{
public string MethodName { get; } = methodName;
}
```

### Usage example

```csharp
public class C
{
[Lazy(nameof(CalculateHeavyName))]
public partial string HeavyName { get; }

// assume heavy calculation here
private string CalculateHeavyName() => string.Empty;
}
```

### Breaking change?

No

### Alternatives

As listed above, Lombok.NET offers a source generator for generating lazily-calculated instances. To avoid conflicts with Lombok's `Lazy`, we could provide an alternative name to the attribute.

### Additional context

_No response_

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