Add PiExample and PiExampleFluent tests; extract shared test helpers

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The test suite only covered the simple ColorsClass pattern. This adds coverage for the attribute-based switch pattern (SwitchCase/SwitchDefault) and the fluent generator API (Generator.MethodImplementation<TArg, TReturn>().WithSwitchBody()...), while eliminating duplication across test helpers.

Changes

• GeneratedCodeTestHelper (new) — centralizes FindProjectDirectory() and ReadGeneratedCode(fileName) previously duplicated inline in UnitTest1
• TestSlowMath (new) — Pi-digit lookup shared by both Pi test classes, mirrors SlowMath from Examples
• PiExampleTests (new) — TestPiClass mirrors PiExample using [SwitchCase]/[SwitchDefault] attributes; tests verify both runtime values and exact generated switch source
• PiExampleFluentTests (new) — TestPiFluentClass mirrors PiExampleFluent using the fluent API with Integer.Range(300, 303); tests cover the expanded case set (0–2, 300–303) and default fallback
• UnitTest1 (refactored) — drops the now-redundant private helpers in favour of GeneratedCodeTestHelper

Each new test fixture has parameterized runtime-output tests and a generated-code assertion:

// Attribute-based switch pattern
[GeneratesMethod(nameof(GetPiDecimal))]
[SwitchCase(arg1: 0)]
[SwitchCase(arg1: 1)]
[SwitchCase(arg1: 2)]
static int GetPiDecimal_Generator_Specialized(int decimalNumber) =>
    TestSlowMath.CalculatePiDecimal(decimalNumber);

// Fluent API pattern
[GeneratesMethod(nameof(GetPiDecimal))]
static IMethodImplementationGenerator GetPiDecimal_Generator() =>
    Generator
        .MethodImplementation<int, int>()
        .WithSwitchBody()
        .ForCases(0, 1, 2, Integer.Range(300, 303)).CompileTimeBody(decimalNumber => TestSlowMath.CalculatePiDecimal(decimalNumber))
        .ForDefaultCase().RuntimeBody(decimalNumber => () => TestSlowMath.CalculatePiDecimal(decimalNumber));

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tests for similar case as PiExample</issue_title>
<issue_description>Re-use code from other tests. Refactor to avoid duplication, create helper code if needed.

After doing that, also add tests for PiExampleFluent. Also re-factor and re-use as needed.</issue_description>

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

• Fixes Add tests for similar case as PiExample #11

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Pull request overview

This PR expands the test suite to cover both attribute-based and fluent API code generation patterns while eliminating test code duplication. The PR mirrors the PiExample and PiExampleFluent examples from the Examples project, creating comprehensive test coverage for switch-based method generation with compile-time and runtime branches.

Changes:

• Extracted shared test helpers (GeneratedCodeTestHelper, TestSlowMath) to eliminate duplication and provide reusable test infrastructure
• Added PiExampleTests covering attribute-based [SwitchCase]/[SwitchDefault] pattern with tests for cases 0-2 (compile-time) and 5 (runtime)
• Added PiExampleFluentTests covering fluent API pattern with Integer.Range() support, testing cases 0-2, 300-303 (compile-time) and 5 (runtime)

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
MattSourceGenHelpers.Tests/GeneratedCodeTestHelper.cs	Centralized helper for locating and reading generated .g.cs files with improved error messages
MattSourceGenHelpers.Tests/TestSlowMath.cs	Pi digit calculation utility mirroring Examples/SlowMath.cs for test isolation
MattSourceGenHelpers.Tests/PiExampleTests.cs	Test fixture for attribute-based switch generation pattern with runtime and generated-code assertions
MattSourceGenHelpers.Tests/PiExampleFluentTests.cs	Test fixture for fluent API switch generation with Integer.Range support and comprehensive case coverage
MattSourceGenHelpers.Tests/UnitTest1.cs	Refactored to use GeneratedCodeTestHelper, removing duplicate helper methods

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