ETR01SDK-487: Prepare STM32 examples

[andreondra]

Description

This PR adds STM32 examples. Majority of the content is migrated from the libtropic-stm32 repo.

As we discussed, I duplicated not only boilerplate code, but also vendor code. Due to this, the PR is massive even though I tried to significantly reduce vendor stuff. A lot of code repeats and is basically unchanged from the state in libtropic-stm32 or STM32 vendor repos, as such it's mainly important to review main.h/main.c, CMakeLists.txt, CI, docs.

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Type of Change

Select the type(s) that best describe your change:

• 🐛 Bug fix
• ✨ New feature
• 🧹 Code cleanup or refactoring
• 📝 Documentation update
• 🔧 Build system or toolchain update
• 🔒 Security improvement
• Other (please describe):

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Checklist

Before submitting, please confirm that you have completed the following:

• I opened the Pull Request to the develop branch
• I followed the project's code guidelines
• I formatted the code using clang-format with the recommended configuration
• I updated the changelog, or this change does not require it (e.g., internal or non-functional update)
  • changelog would be updated for all monorepo changes at once
• The project builds without errors or warnings
• I have verified the functionality against the hardware/model as applicable
• I have ensured that public APIs remain backward compatible (if applicable)
• This PR is ready for review by maintainers (no WIP commits left) and marked as Ready for Review

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• Measure Test Coverage

[medexs]

Just a few comments.