build: configure GitHub Copilot coding agent environment

[Copilot]

The GitHub Copilot coding agent needs a pre-configured environment to build this project: system libs, pinned Rust toolchain, protoc, and a pre-build pass to handle tenderdash-proto-compiler downloading Tenderdash sources (which requires internet access unavailable inside the agent's sandboxed session).

Changes

• .github/workflows/copilot-setup-steps.yml — new workflow; job name copilot-setup-steps is required by Copilot:
  • Installs apt deps: build-essential, pkg-config, clang, cmake, libsqlite3-dev (matching other project workflows)
  • Installs Rust 1.92 via actions-rs/toolchain@v1 with rustfmt + clippy components (matching clippy.yml)
  • Caches Cargo registry via actions/cache@v4 with the same key/path as tests.yml/clippy.yml
  • Installs protoc v25.2 using the same script as tests.yml/clippy.yml
  • Runs cargo build -p tenderdash-proto --locked via actions-rs/cargo@v1 to trigger the tenderdash-proto build script, which downloads Tenderdash proto sources — targeted to just the package that needs internet, not the full workspace
  • pull_request trigger (path-filtered) enables testing the workflow via PRs
  • contents: read permission scope

Original prompt

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This section details on the original issue you should resolve

<issue_title>build: configure GitHub copilot environment</issue_title>
<issue_description>We need to configure GitHub copilot environment so that it can build the project successfully.

We need to install protoc from GitHub project, install apt dependencies and rust.

Check GitHub workflows for details.

We also need to build rs-tenderdash-abci outside the sandbox, as it is downloading Tenderdash sources. Alternatively, we can download Tenderdash sources and put them to correct location - verify build.rs from dashpay/rs-tenderdash-abci project; in this case, we need to inspect rs-tenderdash-abci dependency at runtime to determine correct version of tenderdash to download.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes build: configure GitHub copilot environment #741

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[Copilot]

Pull request overview

Adds a dedicated GitHub Actions workflow to provision the GitHub Copilot coding agent environment with required system dependencies, Rust toolchain, protoc, and a pre-build step intended to run the Tenderdash proto download outside the sandboxed agent session.

Changes:

• Introduces .github/workflows/copilot-setup-steps.yml with the required copilot-setup-steps job.
• Installs Linux build dependencies, Rust 1.92 (with clippy/rustfmt), and protoc v25.2.
• Attempts to pre-build tenderdash-proto to trigger Tenderdash proto source download before the agent runs.

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