Build fixes & cleanup in Makefile and CI

[andrei-marinica]

What changed in this PR

Updates Rust 1.98 pinning, CI/Docker build workflows, local artifact reproduction, and C API header formatting.

Changes:

• Pins Rust across toolchains, Docker, and CI.
• Adds unified multi-architecture Docker and local build targets.
• Regenerates the C API header and cleans repository ignore files.

[Copilot]

Copilot review overview

🟡 Changes recommended

Preserve public C API tags and move the macOS platform check before the host build.

Review effort: Lite
Findings: 1 · 1

Open (2)

• Preserve C typedef tags to avoid breaking consumers · New
• Run platform check before expensive Cargo build · New

What changed in this PR

Updates Rust 1.98 pinning, CI/Docker build workflows, local artifact reproduction, and C API header formatting.

Changes:

• Pins Rust across toolchains, Docker, and CI.
• Adds unified multi-architecture Docker and local build targets.
• Regenerates the C API header and cleans repository ignore files.

File	Summary
rust-toolchain.toml	Pins the Rust toolchain.
README.md	Documents local CI artifact reproduction.
Makefile	Adds platform and Docker build targets; macOS checks currently run after host compilation.
Docker/​linux.dockerfile	Provides unified multi-architecture Linux builds.
Docker/​arm64.dockerfile	Removes the superseded ARM Dockerfile.
c-api/​libvmexeccapi.h	Regenerates and reformats C API declarations.
c-api/​build.rs	Configures header formatting; tag removal causes a critical public API break.
.gitignore	Adds editor and OS exclusions.
.github/​workflows/​rust-ci.yml	Pins CI checks to Rust 1.98.
.github/​workflows/​libvmexeccapi-build.yml	Updates native artifact builds.
.github/​workflows/​libvmexeccapi-build-linux-arm64.yml	Uses the unified Linux Docker build.
.dockerignore	Reduces Docker build context.

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