Reduce CI workflow duplication with a reusable composite action

[Devansh-567]

Summary

Several CI workflows contain nearly identical setup steps for building p4c:

• Checkout repository with recursive submodules
• Configure ccache
• Run tools/ci-build.sh

This pattern appears in multiple workflows, including:

• ci-lint.yaml
• ci-p4tools.yml
• ci-ptf.yml
• ci-static-build-test.yml
• ci-validation-nightly.yml
• ci-test-debian.yml
• and others

Proposal

Introduce a reusable composite action under:

.github/actions/setup-p4c-build/action.yml

to encapsulate common setup logic.

Example:

name: Setup p4c build environment

inputs:
  ccache-key:
    required: true

runs:
  using: composite
  steps:
    - uses: actions/checkout@v6
      with:
        submodules: recursive

    - uses: hendrikmuhs/ccache-action@v1
      with:
        key: ${{ inputs.ccache-key }}-${{ runner.os }}
        max-size: 1000M

Workflows would then invoke the composite action and keep only workflow-specific build and test steps.

Benefits

• Reduces duplicated CI configuration.
• Makes future CI updates easier (e.g. cache configuration changes).
• Lowers the risk of workflow drift between jobs.
• Improves maintainability by centralizing common setup logic.

Expected Changes

• Add .github/actions/setup-p4c-build/action.yml.
• Migrate affected workflows to use the composite action.
• Preserve existing workflow behavior and cache keys.
• Reduce duplicated CI setup code across the repository.