Remove unused prover9 dependency

[Copilot]

This PR removes the unused .prover9 directory and its contents from the repository to clean up the codebase.

The .prover9 directory contained historical mace4/prover9 formulas and configuration files that were used for antimagma classification. However, as noted in the directory's own README:

Although, a complete antimagmas enumeration is already available in the package.

Since the package now provides complete antimagma enumeration functionality directly, these external prover9/mace4 files are no longer needed and can be safely removed.

Changes made:

• Deleted .prover9/README.md
• Deleted .prover9/antimagma.in

Verification:

• Confirmed no other files in the repository reference the .prover9 directory or prover9/mace4 tools
• All core package functionality remains intact
• No breaking changes to the API or existing features

This cleanup reduces repository size and removes an unused dependency as requested.

Fixes #44.

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