Prepare package for public release under MIT license

[MidnightDesign]

Summary

• Add MIT LICENSE file (copyright Datascroll Eventsupport GmbH)
• Add README.md with installation instructions and quick-start examples for TestLogger and TestHttpClient
• Add doc/TestSoapClient.md — the only test double that was missing documentation
• Update composer.json: license → MIT, add description and keywords, remove private Eventjet Composer repo (no longer needed since eventjet/coding-standard is on Packagist)
• Replace delegated CI workflow with a self-contained, split workflow: separate jobs for dep check, code style, Psalm, PHPStan, tests (PHP 8.3/8.4/8.5 matrix), and mutation testing
• Coverage is generated once in the PHP 8.3 tests job and reused in the mutation job via artifact
• Pin phpVersion: 8.3 in PHPStan and Psalm configs for deterministic stub selection

Test plan

• All CI jobs pass (deps, cs, psalm, phpstan, tests ×3, mutation)
• LICENSE present and correct
• README.md renders correctly on GitHub
• composer validate passes

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Prepares the eventjet/test-double PHP library for public release by adding licensing and documentation, polishing package metadata, and modernizing CI for a public/open-source workflow.

Changes:

• Add MIT licensing and public-facing docs (README.md, doc/TestSoapClient.md).
• Update composer.json metadata for Packagist (license/description/keywords) and remove the private Composer repository.
• Replace the delegated CI workflow with explicit jobs for dependency checks, style, static analysis, tests (matrix), and mutation testing; pin static analysis PHP version.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/unit/TestSoapClientTest.php	Minor formatting adjustment in a data provider test case.
psalm.xml	Pins Psalm’s PHP version to 8.3 for deterministic analysis.
phpstan.neon.dist	Pins PHPStan’s PHP version to 8.3 (80300).
doc/TestSoapClient.md	Adds missing documentation for TestSoapClient usage and matchers.
composer.json	Sets MIT license, adds metadata, removes private repository configuration.
README.md	Adds installation instructions and quick-start examples.
LICENSE	Adds MIT license text and copyright notice.
.github/workflows/checks.yml	Introduces self-contained CI pipeline with split jobs and coverage artifact reuse.

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