Support for result builder in concat and merge

[DevYeom]

Related Issues 💭

Description 📝

• Expand the functionality of EffectsBuilder proposed in Add effects result builder for sugar #68 .
• Add unit tests for EffectsBuilder.

Additional Notes 📚

.concat {
    .just(.increment)
    .just(.increment)
    if condition {
        .just(.increment)
    }
}

Checklist ✅

• If it's a new feature, have appropriate unit tests been added?
• If the changes affect existing functionality, please verify whether the above information has been appropriately described.

[DevYeom]

@sobabear FYI

[sobabear]

Thanks!