WIP: Nix build system

.github/actions/build_nix/action.yml

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+name: Build/Cache Nix
+description: Builds default devShell for a platform, caching the results (if applicable)
+inputs:
+  cachix_cache:
+    description: "The name of the Cachix cache to download to and/or upload from"
+    required: true
+    default: "openlane"
+  cachix_token:
+    description: "An authentication token for Cachix"
+    required: false
+    default: ""
+  shell:
+    description: "Shell to use"
+    required: true
+    default: "bash"
+  nix_system:
+    description: "The nix platform string to build for"
+    required: true
+    default: "x86_64-linux"
+  local_cache_key:
+    description: Key to use for the cache
+    required: false
+    default: ""
+  run_tests:
+    description: Whether to run unit tests and the smoke test
+    required: false
+    default: "false"
+runs:
+  using: "composite"
+  steps:
+    - id: cache
+      name: Cache Derivation
+      uses: actions/cache@v3
+      with:
+        key: ${{ inputs.local_cache_key }}-${{ inputs.nix_system }}
+        path: /tmp/${{ inputs.local_cache_key }}
+    - id: Build
+      name: Build
+      shell: ${{ inputs.shell }}
+      run: |
+        substituters='https://${{ inputs.cachix_cache }}.cachix.org https://cache.nixos.org'
+        if [ '${{ inputs.local_cache_key }}' = '' ]; then
+          substituters="file:///tmp/${{ inputs.local_cache_key }} $substituters"
+        fi
+        echo "#################################################################"
+        outPath=$(nix build\
+          --print-out-paths\
+          --no-link\
+          --accept-flake-config\
+          --option system ${{ inputs.nix_system }}\
+          --extra-platforms ${{ inputs.nix_system }}\
+          --option substituters "$substituters"\
+          .#devShells.${{ inputs.nix_system }}.default)
+        echo "out-path=$outPath" >> $GITHUB_OUTPUT
+        sudo du -hs /nix/store/* | sort -h | tail -n 20
+    - name: Unit/Step Tests
+      shell: ${{ inputs.shell }}
+      if: inputs.run_tests == 'true'
+      run: echo TODO
+    - name: Smoke Test
+      shell: ${{ inputs.shell }}
+      if: inputs.run_tests == 'true'
+      run: |
+        echo "#################################################################"
+        nix run\
+          --option system ${{ inputs.nix_system }}\
+          --extra-platforms ${{ inputs.nix_system }}\
+          --accept-flake-config\
+          .#packages.${{ inputs.nix_system }}.cace -- --help
+    - name: Push to local cache
+      shell: ${{ inputs.shell }}
+      if: inputs.local_cache_key != '' && steps.cache.outputs.cache-hit != 'true'
+      run: |
+        nix copy\
+          --to 'file:///tmp/${{ inputs.local_cache_key }}?compression=zstd&parallel-compression=true'\
+          ${{ steps.build.outputs.out-path }}
+    - name: Install + Push to Cachix
+      shell: ${{ inputs.shell }}
+      if: ${{ inputs.cachix_token != '' }}
+      run: |
+        echo "#################################################################"
+        nix-env -iA cachix -f https://cachix.org/api/v1/install
+        cachix authtoken ${{ inputs.cachix_token }}
+        cachix push ${{ inputs.cachix_cache }} ${{ steps.build.outputs.out-path }}

.github/actions/check_space/action.yml

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+name: Check Space
+description: Reusable step that prints disk usage information
+runs:
+  using: "composite"
+  steps:
+    - name: Check Space
+      shell: bash
+      run: |
+        if test -d /nix/store; then
+          sudo du -hs /nix/store/* | sort -h | tail -n 10
+        fi
+        echo ===============
+        df -h
+        echo ===============
+        du -hs ~/* | sort -h
+        echo ===============
+        du -hs * | sort -h
+        echo ===============
+        du -hs /home/runner/runners/* | sort -h
+        echo ===============
+        du -hs /home/runner/work/* | sort -h
+        echo ===============

.github/actions/setup_env/action.yml

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+name: Set up environment
+description: Sets up a number of environment variables that are useful for publishing
+runs:
+  using: "composite"
+  steps:
+    - name: Export Repo URL
+      shell: bash
+      run: echo "REPO_URL=https://github.com/${{ github.repository }}.git" >> $GITHUB_ENV
+
+    - name: Export Branch Name
+      shell: bash
+      run: echo "BRANCH_NAME=${GITHUB_REF##*/}" >> $GITHUB_ENV
+
+    - name: Set default for env.NEW_TAG
+      shell: bash
+      run: echo "NEW_TAG=NO_NEW_TAG" >> $GITHUB_ENV
+
+    - name: Check for new version
+      if: ${{ github.event_name == 'push' && env.BRANCH_NAME == 'main' }}
+      shell: bash
+      run: |
+        python3 ./.github/scripts/generate_tag.py
+
+    - name: Publish
+      if: ${{ github.event_name == 'push' && env.BRANCH_NAME == 'main' && env.NEW_TAG != 'NO_NEW_TAG' }}
+      shell: bash
+      run: |
+        echo "PUBLISH=1" >> $GITHUB_ENV