Extend ffi

[VPRamon]

This pull request significantly enhances the FFI (Foreign Function Interface) API of the tempoch-ffi crate by introducing type-safe duration and difference operations using the QttyQuantity type from the new qtty-ffi dependency. It also improves error safety across the API by wrapping FFI functions with a panic-catching macro, and updates FFI bindings and documentation accordingly.

The most important changes are:

Typed Duration and Difference API (QttyQuantity support)

• Added new FFI functions that compute differences and perform arithmetic on Julian Dates and Modified Julian Dates using QttyQuantity, providing unit-aware, type-safe results (e.g., tempoch_jd_difference_qty, tempoch_jd_add_qty, tempoch_mjd_difference_qty, tempoch_mjd_add_qty, tempoch_jd_julian_centuries_qty, tempoch_period_mjd_duration_qty). [1] [2]
• Updated Cargo.toml to add qtty-ffi as a dependency and bump qtty to version 0.3.1.

FFI Safety and Error Handling

• Introduced a catch_panic! macro to catch Rust panics and return error codes instead of unwinding across the FFI boundary, and applied it to all FFI functions that write to out-pointers or perform conversions. [1] [2] [3] [4] [5] [6] [7]

FFI Bindings and Header Updates

• Updated cbindgen.toml and the generated C header (tempoch_ffi.h) to include qtty_ffi.h for type definitions, exclude duplicate types from auto-generation, and document the new API surface. [1] [2] [3]

Documentation Improvements

• Improved crate-level documentation to explain the new type-safe duration API and the use of QttyQuantity in FFI.

These changes provide a safer, more expressive, and unit-aware FFI API for time computations, facilitating better integration with C/C++ consumers.

[github-actions]

Package	Line Rate	Complexity	Health
tempoch-core.src	99%	0	✔
tempoch-ffi.src	81%	0	✔
Summary	95% (1620 / 1705)	0	✔