code quality: declare strict / inline types

[justlevine]

What?

This PR

1. Adds declare( strict_types=1 ); to plugin files
2. Inlines property types
3. Marks Feature_Loader and Feature_Registry final
4. Updates the Example_Feature to use {@inheritDoc}

Why?

Stricter/native types improve DX by erroring early, saving unnecessary code review and reducing the likelihood of shipping bugs into a release.

How?

See copilot summary.

Testing Instructions

1. See the lints and tests passing.

Testing Instructions for Keyboard

N/a

Screenshots or screencast

Before	After

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Co-authored-by: justlevine <justlevine@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>

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[Copilot]

Pull Request Overview

This PR modernizes the codebase by adding PHP strict type declarations and type hints across all core files, improving type safety and code quality.

Key Changes:

• Added declare(strict_types=1) to all PHP files for strict type checking
• Added type declarations to all class properties (string, bool, array, and fully-qualified class types)
• Marked Feature_Registry and Feature_Loader classes as final to prevent inheritance
• Replaced verbose docblock descriptions with {@inheritDoc} tags in Example_Feature for inherited methods

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
includes/bootstrap.php	Added strict types declaration
includes/Features/Example_Feature/Example_Feature.php	Added strict types declaration and updated docblocks to use {@inheritdoc} for inherited methods
includes/Feature_Registry.php	Added strict types declaration, marked class as final, and added array type to $features property
includes/Feature_Loader.php	Added strict types declaration, marked class as final, and added type declarations to $registry and $initialized properties
includes/Exception/Invalid_Feature_Metadata_Exception.php	Added strict types declaration
includes/Exception/Invalid_Feature_Exception.php	Added strict types declaration
includes/Contracts/Feature.php	Added strict types declaration
includes/Abstracts/Abstract_Feature.php	Added strict types declaration and type declarations to all properties ($id, $label, $description, $enabled)

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