Add slice functions to c-api

[bschoenmaeckers]

Summary by CodeRabbit

• New Features
  • Public API expanded to include slice object handling, exposing creation, unpacking, and index-adjustment entrypoints for external callers.
  • Added a const constructor and const accessors for saturated slice values to inspect slice parameters reliably.
  • Slice-related utilities now available for integration and interoperability with external components.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: fa12ac68-9c41-41b0-9a82-e5d80a83aeec

📥 Commits

Reviewing files that changed from the base of the PR and between 5947a89 and d984640.

📒 Files selected for processing (3)

• crates/capi/src/lib.rs
• crates/capi/src/sliceobject.rs
• crates/vm/src/sliceable.rs

✅ Files skipped from review due to trivial changes (1)

• crates/capi/src/lib.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• crates/capi/src/sliceobject.rs
• crates/vm/src/sliceable.rs

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📝 Walkthrough

Walkthrough

Adds a new sliceobject capi module and three FFI functions—PySlice_New, PySlice_Unpack, PySlice_AdjustIndices—plus const accessors on SaturatedSlice; includes disabled PyO3 unit tests for slice index behavior.

Changes

Slice FFI Implementation

Layer / File(s)	Summary
SaturatedSlice public API crates/vm/src/sliceable.rs	SaturatedSlice gains a const from_parts() constructor and const start(), stop(), step() getters marked #[must_use], enabling construction and inspection of slice components without direct field access.
PySlice FFI functions and tests crates/capi/src/sliceobject.rs	Adds three FFI entrypoints: PySlice_New (build PySlice from nullable PyObject* inputs), PySlice_Unpack (downcast and write saturated start/stop/step to isize* outputs), and PySlice_AdjustIndices (saturate and adjust indices for a given length, handling negative step specially). Contains PyO3-based unit tests currently gated by #[cfg(false)].
Module export crates/capi/src/lib.rs	Declares and publicly exports the sliceobject module in the capi crate.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• youknowone
• ShaharNaveh

Poem

🐰
I nibbled at indices, tuned every part,
From null to None, I stitched slice art.
Const bits in order, adjusted with care,
C callers and VM now dance in the air.
Hop—FFI slices land safely, fair.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add slice functions to c-api' clearly and concisely describes the main change: adding three FFI functions (PySlice_New, PySlice_Unpack, PySlice_AdjustIndices) to the C API surface.
Docstring Coverage	✅ Passed	Docstring coverage is 90.91% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ShaharNaveh]

The capi looks clean 🚀