Improve README with badges, devcontainer info, tests, coverage, and CI documentation

[Copilot]

• Add CI/CD pipeline status badge
• Add license badges
• Add documentation about devcontainer usage
• Add documentation about nix shell (not present in repo - skipped)
• Add documentation about Kani verification (proofs)
• Add documentation about tests
• Add documentation about coverage
• Add brief overview of repository structure (expanded existing section)
• Add CI/CD pipeline overview section
• Remove accidentally added submodules
• Clean up branch to be based on main

Original prompt

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This section details on the original issue you should resolve

<issue_title>General: Improve Readme</issue_title>
<issue_description>The current readme is lacking information. Especially regarding devcontainer, nix shell, proofs, tests, coverage.
Additionally the following parts should be added:

• Badges for pipeline state.
• Brief overview about the repo structure.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes General: Improve Readme #15

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[xarantolus]

@copilot Remove submodules / rebase on master

[Copilot]

@copilot Remove submodules / rebase on master

I've removed the submodules in commit 35fad9c.

However, to properly rebase on main (which would require rewriting history and force-pushing), I don't have the necessary permissions. The branch currently has the following commits:

• 313d22d: "Use CMD instead of entrypoint" (contains submodules)
• d330710: "Initial plan"
• e601a3d: "Improve README with badges..." (the actual changes)
• 35fad9c: "Remove submodules" (cleanup)

Main has commit 4297ec1 which is the clean version of 313d22d without submodules. Would you prefer to:

1. Manually rebase this branch on main (since it requires force-push), or
2. Accept the current solution where the submodules are removed in a subsequent commit?

The final diff against main is clean - only README changes with no submodules.