chore: sync-lockfiles use 1.93.0 by default

[diogomatsubara]

• zenoh defaults to 1.93.0 so the sync-lockfiles requires this update since the change in separate support of rust 1.75 to avoid build issues zenoh#2392
• removes the copying of the zenoh-c Cargo.lock to the opaque-types dir because when zenoh-c rectifies its lockfile, the build script copies it over to the opaque-types dir.

This should fix https://github.com/eclipse-zenoh/zenoh/actions/runs/22267474383/job/64416243684 and is related to eclipse-zenoh/zenoh#2439

[Copilot]

Pull request overview

Updates the sync-lockfiles GitHub Actions workflow to use Rust 1.93.0 by default, aligning the lockfile sync process with Zenoh’s updated default toolchain.

Changes:

• Bump the default Rust toolchain used by sync-lockfiles from 1.75.0 to 1.93.0 (inputs description + all rustup/cargo invocations).
• Remove the zenoh-c-specific step that copied Zenoh’s Cargo.lock into build-resources/opaque-types/Cargo.lock.

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