chore: bump to Lean 4.26

[RSoulatIOHK]

Very minimal bump to ensure building and no deprecation warnings

Description

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update
• Performance improvement
• Code refactoring
• Test updates

Related Issue

Use any of the following for our ticket management to know which tickets to move to Done when PR is merged:

• Fixes #(issue number)
• Closes #(issue number)

Changes Made

• Updated the Lean toolchain from version v4.25.0 to v4.26.0 in lean-toolchain, ensuring compatibility with the latest features and bug fixes.

• In Blaster/Optimize/Rewriting/OptimizeString.lean, corrected the string construction in normStringValue by replacing String.mk elms.toList with String.ofList elms.toList as the former was being deprecated. Followed the tip given by the deprecation message.

Testing

Test Coverage

• Added new tests for new functionality
• Updated existing tests
• All tests pass locally
• For bug fixes: Added example to Tests/Issues/ folder

Documentation

• README updated (if applicable)
• Code comments added/updated
• Doc comments added for new optimization/rewritting rules

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes using make check_all
• For bug fixes: Original failing example added to Tests/Issues/ folder with reference to issue number

Additional Notes