Make XSD as powerful and as restrictive as possible

[yegor256]

Currently, we use XSL in order to check the consistency of XMIR. Let's try to use XSD features for this task instead.

[github-actions[bot]]

@yegor256 thanks for the report, here is a feedback:

Problems

• The report does not have an informative title: The current one seems more like a suggestion than an actual summarization of the issue.
• The bug's description is unclear: It fails to precisely define the issue with the current utilization of XSL and the reasons why XSD features would be better.
• Insufficient context: The report falls short of providing enough context or background details. It leaves us uninformed about what XMIR is and the necessity for its consistency check.

I would recommend adding a concise, informative title to the bug report to effectively summarize the main issue.

Please fix the bug report in order it to get resolved faster. Analyzed with gpt-4