Implement wp site get command to enable site operations by URL

[Copilot]

• Understand existing codebase and site command structure
• Implement wp site get command that accepts site ID or URL
• Add support for fetching site by URL (domain/path lookup)
• Add proper field formatting with WP_CLI\Formatter
• Create Behat tests for the new command
• Test the command with various scenarios (ID, URL, field output)
• Update documentation with usage examples
• Run code quality checks (lint, phpcs, phpstan)
• Verify all site.feature tests pass
• Address code review feedback (refactor field casting, improve test reliability)
• Use WordPress's cached get_blog_id_from_url() function for URL lookups

Original prompt

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This section details on the original issue you should resolve

<issue_title>site delete: allow deleting a site with the --url option</issue_title>
<issue_description>## Feature Request

• Yes, I reviewed the contribution guidelines.

Describe your use case and the problem you are facing

Currently the blog ID or slug must be specified when using the command. In cases where a custom domain is used, however, the --slug option fails and it is tedious to look up the assigned site ID in an automated use case.

Describe the solution you'd like

Allow site deletion by only specifying the --url option. For example: wp site delete --url="http://example.com".
</issue_description>

Comments on the Issue (you are @copilot in this section)

@swissspidy We could implement `wp site get ` instead, then one could pair `wp site delete` with `wp site get http://example.com --field=id`. This would be more in line with all the other commands.

• Fixes site delete: allow deleting a site with the --url option #506

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[codecov]

Codecov Report

❌ Patch coverage is 87.09677% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/Site_Command.php	87.09%	4 Missing ⚠️

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