refactor: improve setup-wsl action to support native Windows testing

Instead of building inside WSL on the host disk, we should build inside
the WSL file system as that is significantly faster and avoids the
interop bottleneck. For this, we naively copy over the repository after
checkout into WSL; and operate from in there.

Pending TODO is how we can properly cache contents inside WSL; as the
cache action currently does not seem to pick it up properly.

Author: devversion

github-actions/setup-wsl/action.yml

@@ -36,7 +36,7 @@ outputs:
     description: UNC Windows path pointing to the WSL file system root.
     value: \\\\wsl.localhost\Debian
   repo_path:
-    description: Path to the copied repository directory
+    description: Path to the copied repository directory (as Unix wsl path)
     value: ${{steps.disk_path.outputs.repo}}
 
 runs:
@@ -46,7 +46,7 @@ runs:
     # Note: `memory` by default is 50% of the Windows host machine. We want to try
     # a higher percentage to leverage more of the GitHub Windows machines.
     # They have 16GB by default. See: https://docs.github.com/en/actions/using-github-hosted-runners/using-github-hosted-runners/about-github-hosted-runners.
-    - uses: Vampire/setup-wsl@v4
+    - uses: Vampire/setup-wsl@v5
       with:
         wsl-conf: |
           [interop]
@@ -100,9 +100,11 @@ runs:
       env:
         WSLENV: 'GITHUB_OUTPUT/p'
       run: |
-        mkdir $HOME/repo
-        cp -R ./* $HOME/repo/
-        echo "repo=$(wslpath -w $HOME/repo)" >> $GITHUB_OUTPUT
+        repo_path="$HOME/repo"
+        cp -R . $repo_path
+
+        echo "repo=$repo_path" >> $GITHUB_OUTPUT
+        echo "Repo path is: $repo_path"
 
     - name: Cache for nvm, yarn profile caches.
       uses: actions/cache@v4
@@ -115,17 +117,18 @@ runs:
           ${{ runner.os }}-wsl-cache-v${{inputs.cache_version}}-
 
     - name: Setup nvm
-      working-directory: ${{steps.paths.outputs.repo}}
       shell: wsl-bash {0}
       run: |
         curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/master/install.sh | bash
         export NVM_DIR="$HOME/.nvm"
         # Note: Specify `--install` due to https://github.com/nvm-sh/nvm/issues/1985.
         [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" --install
 
-    - run: nvm install
-      working-directory: ${{steps.paths.outputs.repo}}
+    - name: Installing Node and npm (in WSL)
+      run: |
+        cd ${{steps.disk_path.outputs.repo}}
+        nvm install
       shell: wsl-bash {0}
-    - run: npm install -g yarn@1
-      working-directory: ${{steps.paths.outputs.repo}}
+    - name: Installing Yarn (in WSL)
+      run: npm install -g yarn@1
       shell: wsl-bash {0}