feat: Custom instructions in executor

[dima74]

Description

Added ISI for custom instructions, and two tests demonstrating possible use:

• Test with one custom instruction MintAssetForAllAccounts
• Test with simple expression system

Linked issue

Closes #4599

Benefits

Checklist

• [x] I've read CONTRIBUTING.md
• [x] I've used the standard signed-off commit format (or will squash just before merging)
• [ ] All applicable CI checks pass (or I promised to make them pass later)
• [ ] (optional) I've written unit tests for the code changes
• [ ] I replied to all comments after code review, marking all implemented changes with thumbs up