Evaluate the infection/infection dev dependency

[TravisCarden]

• Part of https://github.com/php-tuf/composer-stager/issues/78.

Dependency	infection/infection
Description	Mutation testing framework.
Value/justification	High. This helps find gaps and inadequacies in automated tests--not merely in code coverage but in logical and implicit change vectors. It has already led to meaningful improvement in tests. It is currently running on CI, where it displays results and comments on PRs but doesn't fail builds.
Usage/popularity	Very high. Currently over 10M installs and 1K dependents on Packagist.
Security policy	None that I can find.
Maintainance	Active. Responsive maintainers. Regular, well-documented releases adhere strictly to Semver.
Considerations	Previous discussion in https://github.com/php-tuf/composer-stager/issues/56

Dependency tree

$ composer info --tree infection/infection
infection/infection 0.27.7 Infection is a Mutation Testing framework for PHP. The mutation adequacy score can be used to measure the effectiveness of a test set in terms of its ability to detect faults.
|--colinodell/json5 ^2.2
|  |--ext-json *
|  |--ext-mbstring *
|  |  `--php >=7.1
|  `--php ^7.1.3|^8.0
|--composer-runtime-api ^2.0
|--composer/xdebug-handler ^2.0 || ^3.0
|  |--composer/pcre ^1 || ^2 || ^3
|  |  `--php ^7.4 || ^8.0
|  |--php ^7.2.5 || ^8.0
|  `--psr/log ^1 || ^2 || ^3
|     `--php >=8.0.0
|--ext-dom *
|--ext-json *
|--ext-libxml *
|--ext-mbstring *
|  `--php >=7.1
|--fidry/cpu-core-counter ^0.4.0 || ^0.5.0 || ^1.0
|  `--php ^7.2 || ^8.0
|--infection/abstract-testframework-adapter ^0.5.0
|  `--php ^7.4 || ^8.0
|--infection/extension-installer ^0.1.0
|  `--composer-plugin-api ^1.1 || ^2.0
|--infection/include-interceptor ^0.2.5
|--justinrainbow/json-schema ^5.2.10
|  `--php >=5.3.3
|--nikic/php-parser ^4.15.1
|  |--ext-tokenizer *
|  `--php >=7.0
|--ondram/ci-detector ^4.1.0
|  `--php ^7.1 || ^8.0
|--php ^8.1
|--sanmai/later ^0.1.1
|  `--php >=7.4
|--sanmai/pipeline ^5.1 || ^6
|  `--php ^7.4 || ^8.0
|--sebastian/diff ^3.0.2 || ^4.0 || ^5.0
|  `--php >=7.3
|--symfony/console ^5.4 || ^6.0 || ^7.0
|  |--php >=8.1
|  |--symfony/deprecation-contracts ^2.5|^3
|  |  `--php >=8.1
|  |--symfony/polyfill-mbstring ~1.0
|  |  `--php >=7.1
|  |--symfony/service-contracts ^2.5|^3
|  |  |--php >=8.1
|  |  `--psr/container ^2.0
|  |     `--php >=7.4.0
|  `--symfony/string ^5.4|^6.0
|     |--php >=8.1
|     |--symfony/polyfill-ctype ~1.8
|     |  `--php >=7.1
|     |--symfony/polyfill-intl-grapheme ~1.0
|     |  `--php >=7.1
|     |--symfony/polyfill-intl-normalizer ~1.0
|     |  `--php >=7.1
|     `--symfony/polyfill-mbstring ~1.0
|        `--php >=7.1
|--symfony/filesystem ^5.4 || ^6.0 || ^7.0
|  |--php >=8.1
|  |--symfony/polyfill-ctype ~1.8
|  |  `--php >=7.1
|  `--symfony/polyfill-mbstring ~1.8
|     `--php >=7.1
|--symfony/finder ^5.4 || ^6.0 || ^7.0
|  `--php >=8.1
|--symfony/process ^5.4 || ^6.0 || ^7.0
|  `--php >=8.1
|--thecodingmachine/safe ^2.1.2
|  `--php ^8.0
`--webmozart/assert ^1.11
   |--ext-ctype *
   |  `--php >=7.1
   `--php ^7.2 || ^8.0

[TravisCarden]

Infection now runs on its own "Mutation" job and comments on PRs when it detects new issues. It's has proved very helpful.