ci: update crates.io categories to supported slugs and align keywords

[CHINMAYVIVEK]

Summary

This PR updates the Cargo.toml metadata for rust-jpl to use only crates.io-supported categories while maintaining maximum discoverability via keywords.

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Motivation

Previously, publishing failed because categories like astronomy, physics, and astrology are not allowed on crates.io. This change:

• Uses valid category slugs
• Aligns categories with keywords for semantic search relevance
• Keeps the crate discoverable for astronomy, astrophysics, planetary science, astrology, and space simulation audiences

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JPL Context

No direct change to NASA JPL services or datasets. This is a metadata update for publishing and discoverability purposes.

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Type of Change

• Bug fix
• New feature
• Breaking change
• Performance improvement
• Refactor
• Documentation
• Metadata / publishing improvement

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Implementation Notes

• Categories updated to: science, date-and-time, mathematics, simulation
• Keywords updated to: ephemeris, astronomy, astrology, julian-date, jpl
• Maintains max 5 categories and 5 keywords per crates.io rules
• No functional code changes

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Testing

• Manual cargo publish --dry-run verified
• Unit tests
• Integration tests

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API Impact

• No public API changes
• Additive API changes
• Breaking API changes

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Checklist

• cargo fmt
• cargo clippy
• cargo test
• Public APIs documented
• Unsafe code justified or avoided