Add explicit build-for-testing action

[yqiang]

Summary

Please add an explicit XcodeBuildMCP action/CLI tool equivalent to xcodebuild build-for-testing.

Motivation

Today, the CLI exposes build and test actions such as:

xcodebuildmcp simulator build
xcodebuildmcp simulator test
xcodebuildmcp device build
xcodebuildmcp device test
xcodebuildmcp macos build
xcodebuildmcp macos test

For simulator tests, XcodeBuildMCP already appears to use a two-phase flow internally when test preflight is available: build-for-testing followed by test-without-building. However, there does not appear to be a user-facing action that performs only the build-for-testing phase.

This is useful for workflows that want to prepare test bundles once and run tests later or elsewhere, mirroring existing xcodebuild workflows.

Requested behavior

Add a first-class action, for example:

xcodebuildmcp simulator build-for-testing
xcodebuildmcp device build-for-testing
xcodebuildmcp macos build-for-testing

or another naming scheme consistent with the project.

The action should pass through the same core options as the existing build/test commands, including project/workspace path, scheme, configuration, destination, derived data path, and extra xcodebuild args.

Notes

Passing build-for-testing through --extra-args is not equivalent because the existing build command appends its own final build action. A dedicated action would make this behavior discoverable and avoid requiring users to fall back to raw xcodebuild.