`sanity_check` methods throughout the codebase shouldn't be part of the API

Actually I'll just file an issue. There are a lot of sanity_check methods in the code, many of which are not called from within the library, and at least one has a doc example suggesting to use it to check "whether all spend paths are accessible in the Bitcoin network".

So we need to re-assess all these functions and see if they can be pulled into the type system somehow so you simply can't create the objects without running the (non-pub) methods.

Originally posted by @apoelstra in https://github.com/rust-bitcoin/rust-miniscript/pull/652#discussion_r1514517762

まず、コードベース全体にある sanity_check メソッドを一覧化し、Bitcoin の支払いパスに関するドキュメント例を含め、リンクされた pull request の議論を確認します。どのメソッドが外部から呼び出し可能で、どの不変条件を代わりに型システムで強制すべきかを判断します。API が不適切なチェックを公開しなくなり、オブジェクトの有効性が一貫して扱われるようになれば完了です。