chore: Use swatinem/rust-cache action for caching Rust

[Benjamin-Philip]

What's Changed

Uses swatinem/rust-cache for effectively caching Rust. Removes any manual
caching. This will potentially lead to faster CIs since compiling Rust is the
most time intensive common step.

[github-actions]

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[Copilot]

Pull request overview

This PR updates the GitHub Actions workflows to use swatinem/rust-cache for Rust dependency/build caching, replacing the previous manual actions/cache configuration, to reduce CI time spent recompiling Rust NIF code.

Changes:

• Replaces manual Cargo directory caching with swatinem/rust-cache in the Erlang CI workflow.
• Adds Rust toolchain + swatinem/rust-cache steps to the Dialyzer job (to align Rust caching/installation across jobs that compile).
• Updates the Docs workflow to use swatinem/rust-cache for the Rust workspace used during docs generation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/erlang.yml	Switches Rust caching to swatinem/rust-cache and ensures Rust is installed/cached for jobs that compile/dialyze.
.github/workflows/docs.yml	Switches Rust caching to swatinem/rust-cache for the docs build job.

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[kou]

+1

BTW, could you open an issue before you work on something? It's for openness. If we share what we want to do publicly, others may be able to join this project.