Port bug fixes from dev branch to version-3

[zhyian]

Description

Ports bug fixes from the dev branch that also affect version-3. Each fix was manually adapted to version-3 codebase (PHP 7.4+ typed properties, PHPStan, restructured classes).

How has this been tested?

• Existing unit and integration tests updated to reflect the changes
• Verified that each fix addresses the same root cause present in version-3
• Tested with projects on my local setup

Types of changes

Bug fixes

• Env-example step not respecting ENV_DIR configuration (dev commit 1c7c3c6): EnvExampleStep::allowed() and targetPath() now resolve paths using the configured ENV_DIR instead of always using the project root. Added Filesystem::normalizePath() public method to support this.
• Question forcing lowercase on all answers (dev commit 3b92c56): Moved answer filtering logic from Io into Question::filterAnswer(), so strtolower is only applied for standard answer-key matching - not unconditionally on all input.
• Raw string filter for environment variables (dev PR Add a "Raw string" filter, Fix possible inconsistency between constants and environment variables in the generated cache #136): Passwords, secret keys, and salts containing special characters (&, <, ') were corrupted by FILTER_STRING (which runs htmlspecialchars/strip_tags). Added FILTER_RAW_STRING using addslashes() instead, applied to DB_PASSWORD, FTP_PASS, WP_PROXY_PASSWORD, and all AUTH/NONCE/SECRET keys and salts.
• MU plugins loader edge cases (dev commit 48d4844): MU plugins installed via installer-paths (e.g. from wp.org, which can't use the wordpress-muplugin type) were not being loaded. Now scans mu-plugins subdirectories for plugins not covered by known packages, with dropin filtering to avoid double-loading.

New feature

• N/A

Breaking change

• N/A

Issues

• Add a "Raw string" filter, Fix possible inconsistency between constants and environment variables in the generated cache #136
• Related dev commits: 1c7c3c6, 3b92c56, 48d4844

Checklist:

• My code is tested
• My code follows the project code style
• My code has documentation (for new features or changed behavior)