Replace tut with doctest

[bennettgoble]

Problem

The Second Life viewer currently uses the tut unit test framework, which is no longer maintained. As a result, we face several issues:

• Diminishing community support and updates
• Limited features and poor failure diagnostics
• We need to maintain our forked and modified version of tut

Replacing tut with a more modern and maintained framework will improve testability, developer experience, and long-term maintainability.

Solution

Replace tut with doctest, a lightweight, single-header C++ testing framework that offers clearer output, and a more modern and flexible approach to writing and organizing tests.

Migration plan

• Remove the tut dependency from the viewer build.
• Add the doctest header to the viewer repository (as it is header-only).
• Port all existing tut tests to doctest.
• Ensure tests are discoverable and executable via ctest.
• Document the new test framework and example usage for contributor onboarding.
• Ensure CI/CD passes and is correctly integrated with tests

Alternatives considered

• GoogleTest: Heavier and slower to compile; requires linking and additional setup
• Catch2: Similar to doctest but slightly heavier and not header-only in newer versions

Reward

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[bennettgoble]

/reward 150

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🙌 Once your PR is open, comment /claim #4445 either in the PR description or within the comments.

[bennettgoble]

/reward 50

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💪 Comment /try below and start working on it!
🙌 Once your PR is open, comment /claim #4445 either in the PR description or within the comments.

[opirebot]

🎉 The user @JulianJulius has claimed all rewards for this issue.
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[akash1520]

Hi @bennettgoble, is anyone currently working on this issue, or would it be alright if I took it on?

[mayconbekkers]

/try

Check if you're the only one trying 👇

There are already people trying to solve this issue. You're welcome to tackle it independently, but we encourage you to reach out to the contributors that are trying to solve the issue if you'd like to collaborate with them.

The other contributor is: @JulianJulius.