Move calcpi-rs into CalcPi.jl/deps directory

[terasakisatoshi]

Summary

This PR reorganizes the project structure by moving the Rust library from the root directory into , making it a proper dependency of the Julia package.

Changes

1. Directory Structure Reorganization

• Moved →
• All Rust source files, configuration files, and generated headers moved

2. Build Scripts and Path References

• Updated to use instead of
• Updated default path to
• Updated and library search paths

3. CI/CD Updates

• Updated all GitHub Actions workflows to use paths
• Updated cache paths and keys to reflect new location
• Updated integration test paths

4. Documentation Updates

• Updated all path references in documentation
• Updated project structure descriptions
• Updated build instructions and troubleshooting guides

Benefits

• Better project organization: is now clearly a dependency of
• Cleaner root directory structure
• More intuitive for Julia package development workflow
• Follows Julia package conventions for embedded dependencies

Testing

• All path references updated
• Build scripts tested with new paths
• CI workflows updated
• Documentation reviewed for accuracy