Replace self-made Ensure with GSL Expects for preconditions

[konard]

Summary

This PR addresses issue #75 by replacing the self-made Ensure system with the standardized GSL (Guidelines Support Library) Expects for precondition checking.

Changes Made

• Added GSL dependency: Updated CMakeLists.txt and conanfile.txt to include Microsoft GSL library
• Replaced custom preconditions: Changed Ensure::Always::MaximumArgumentIsGreaterOrEqualToMinimum to Expects(maximum >= minimum) in Range[T].h
• Updated build configuration: Added local GSL headers for build compatibility
• Modified tests: Commented out tests that relied on exception throwing behavior since GSL Expects terminates the program instead

Key Behavioral Change

The main behavioral difference is that GSL's Expects terminates the program when preconditions fail, rather than throwing exceptions. This aligns with the C++ Core Guidelines recommendation for contract checking.

Before:

if (Minimum > Maximum) {
    Ensure::Always::MaximumArgumentIsGreaterOrEqualToMinimum(minimum, maximum, "maximum");
}

After:

if (Minimum > Maximum) {
    Expects(maximum >= minimum);
}

Test Plan

• Verified GSL Expects compiles and works correctly
• Confirmed that valid Range construction works as expected
• Verified that invalid Range construction properly terminates (as designed)
• Updated test files to reflect new behavior

🤖 Generated with Claude Code

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Resolves #75