[WIP] Merge with upstream v1.25

[miketlk]

🚧 Work in Progress – Early Draft

This pull request is opened early to:

• Share current progress
• Gather feedback from contributors
• Discuss implementation approaches

💡 Note: This PR is not ready for review or merging. Some parts may be incomplete, untested, or non-buildable at this stage. Feel free to comment on design decisions, request clarifications, or suggest alternatives.

Summary

Upgrade the fork to match upstream release v1.25.

Changes

• Merged upstream v1.25 tag into fork
• Updated Specter-specific add-ons according to the newer APIs and architecture
• Reverted flattened libs back to Git submodules
• Support of the Discovery board was made less interconnected with the general Micropython code

Testing

• Local tests pass with the same result as upstream's v1.25 failing on select_poll_fd
• CI tests need more attention

Checklist

• Code builds without errors
• Tests added or updated
• Documentation updated if necessary