Fix clang-tidy dependency setup

[anutosh491]

Description

As seen in the last 2 prs #493 #492 this job is failing

The clang-tidy job has been failing before CMake or clang-tidy runs because ZedThree/clang-tidy-review@v0.23.1 attempts to install additional APT packages inside its Ubuntu 25.10 container. That installation exits with status 100.

This updates and simplifies the clang-tidy environment setup:

• Remove the unnecessary apt_packages installation.
• Update Micromamba from 1.5.10-0 to 2.8.1-0.
• Verify the downloaded Micromamba binary using its SHA-256 checksum.
• Use micromamba run instead of installing shell hooks and activating the environment.
• Use the Clang 21 compiler provided by environment-dev.yml, matching the clang-tidy 21 toolchain.
• Remove unused host-side Python and LLVM setup.
• Remove the preliminary ignored CMake failure and redundant build cleanup.
• Avoid host/container path assumptions by using relative paths.

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[vgvassilev]

You can take a look how this was done in clad -- we can port the changes here too, I believe.

[anutosh491]

You can take a look how this was done in clad -- we can port the changes here too, I believe.

Ahh okay I can move to how clad does it later. For now my goal is to just fix some issues/ci on xeus-cpp for my talk next week. These changes were some obvious improvements I could see (like moving micromamba from 1.5 to 2.8 etc & also the clang-tidy job was failing anyways). Hopefully this should be fine for now 🙏

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.84%. Comparing base (7267686) to head (3fc0157).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #494   +/-   ##
=======================================
  Coverage   72.84%   72.84%           
=======================================
  Files          18       18           
  Lines        1204     1204           
  Branches      113      113           
=======================================
  Hits          877      877           
  Misses        327      327           

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[JohanMabille]

Let's open an issue to track the port of changes made to clad