Embeddable Once SDK with Rust and Apple support

This release introduces a new embeddable SDK for Once cache access. Rust projects can now depend on the once crate to read and write blobs, as well as manage action-cache entries, through a high-level local cache API. Apple developers can also integrate a released Once.xcframework binary target, exposing Swift-friendly async APIs backed by the same JSON-based C ABI. The release workflow now builds, signs, notarizes, and uploads the XCFramework as a release asset.