CI: verify the macros expansion

[sept-en]

As plugins are expected to be utilized by smart contracts for vital purposes (ownership, upgradability, ACL, etc.), it's mandatory to ensure the validity of possible near-plugins updates. While the target smart contract repository may have its own rules to ensure this, we may have our ways to verify the regression and absence of the introduction of something unexpected. This is achievable to

To achieve this, we need to add additional verification on examples' contracts. Required steps:

• expand the code of each smart-contract example using cargo expand;
• add expanded code (artifact) to the stage;
• expand the code in CI;
• verify the difference between staged and stored artifact source code in CI.

When this is added, this will add also have the following positive effects:

• Examples are always up-to-date: every change in the plugin's functionality will also inherently require updating the source code of appropriate examples.
• The impact of changes is clearly visible: if new functionality is added to the plugins or something is changed, it's clear in the expanded examples' code how exactly this plugin will "unwind" from macroses to source code. Thus it's possible to notice some unexpected behavior or mistakes while reviewing the expanded code.