CLI: add a `run test-expr` to run expressions in test framework without need of a file

Motivation and Context

Looking at issue #1415, it could be interesting to have a CLI sub-command that allows running expressions in test framework without needing to provide a file.

Description

This MR implements such sub-command.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

New sub-command can evaluate expressions directly in the testing framework:

$ ligo run test-expr cameligo "Test.log 42"
42                                          
Everything at the top-level was executed.
- eval exited with value ().

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).