Stabilize prek CI by pinning Rust toolchain resolution

[Copilot]

The prek GitHub Actions job was failing in the cargo fmt hook due to rustup attempting a partial toolchain recovery and hitting a cargo-clippy component conflict. This updates the workflow so prek hooks run against the explicitly pinned Rust toolchain.

• Problem

  • prek run invoked cargo fmt, which resolved through implicit rustup/toolchain behavior and triggered:
    • failed to install component ... clippy-preview ... detected conflict: 'bin/cargo-clippy'

• Change

  • Set a job-level Rust toolchain override in .github/workflows/prek-check.yml:
    • RUSTUP_TOOLCHAIN: 1.92.0
  • This ensures cargo fmt in prek runs against the preinstalled pinned toolchain instead of re-resolving via rustup during hook execution.

• Effect

  • Removes nondeterministic rustup component reconciliation from the prek path.
  • Keeps formatting checks aligned with the intended pinned Rust version.

jobs:
  prek:
    runs-on: ubuntu-latest
    env:
      RUSTUP_TOOLCHAIN: 1.92.0

[Copilot]

Pull request overview

This PR stabilizes the prek GitHub Actions workflow by forcing prek-invoked Rust tooling (notably cargo fmt) to run under an explicitly pinned Rust toolchain, avoiding rustup component conflict/recovery behavior during hook execution.

Changes:

• Add a job-level RUSTUP_TOOLCHAIN: 1.92.0 environment override for the prek job.

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