Implement WithCompileTimeConstants for fluent method body builders

[Copilot]

The WithCompileTimeConstants API had interfaces defined in Abstractions and a CompileTimeConstants slot on BodyGenerationData, but no builder implementations or extractor support.

Stage4 builders → Stage5 transitions

Added WithCompileTimeConstants<TConstants>(Func<TConstants>) to all four Stage4 builders. The factory is invoked immediately and the materialized result stored in BodyGenerationData.CompileTimeConstants. Returns the corresponding Stage5 builder:

• DataMethodBodyBuilderStage5WithConstants<TParam1, TReturnType, TConstants>
• DataMethodBodyBuilderStage5NoArgWithConstants<TReturnType, TConstants>
• DataMethodBodyBuilderStage5ReturnVoidWithConstants<TParam1, TConstants>
• DataMethodBodyBuilderStage5ReturnVoidNoArgWithConstants<TConstants>

BodyGenerationDataExtractor

Updated TryExtractFromConstantFactory and TryExtractFromRuntimeBody to pass CompileTimeConstants as the first argument when the delegate expects a parameter and constants are present. Delegates with additional method parameters beyond constants still correctly return null (can't evaluate at compile time).

Usage

Per PiExampleFluent:

Generate.MethodBody()
    .ForMethod().WithReturnType<int>().WithParameter<int>()
    .WithCompileTimeConstants(() => new
    {
        PrecomputedTargets = keys.ToDictionary(i => i, i => Compute(i))
    })
    .UseProvidedBody((constants, decimalNumber) =>
    {
        if (constants.PrecomputedTargets.TryGetValue(decimalNumber, out int r)) return r;
        return Compute(decimalNumber);
    });

Tests

23 new tests: Stage5 builder wiring, WithCompileTimeConstants data flow, BodyGenerationDataExtractor with/without constants, factory invocation timing, and constant factory priority over runtime body.

Original prompt

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This section details on the original issue you should resolve

<issue_title>WithCompileTimeConstants</issue_title>
<issue_description>There is an skeleton for API WithCompileTimeConstants in the code. However, the implementation of it is unfinished. Look at PiExampleFluent inside PiExample.cs to see how it should be implemented. Finish implementing it. Make sure to use BodyGenerationData to store the constants, no reflection/looking by string shenanigans. </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes WithCompileTimeConstants #97

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