Use composite actions in CI (#65)

* Attempt composite actions in CI

* Remove needs monero-daemon for the action

* Correct actions folder layout

* Remove empty inputs/outputs, add shell

* Try moving env declaration spot

* Remove usage of env

* Cached Rust composite action

* Replace [] with ""

Remove empty outputs

.github/actions/build-dependencies/action.yml

@@ -0,0 +1,25 @@
+name: build-dependencies
+description: Installs build dependencies for Serai
+
+runs:
+  using: "composite"
+  steps:
+    - name: Install solc
+      shell: bash
+      run: |
+        pip3 install solc-select
+        solc-select install 0.8.9
+        solc-select use 0.8.9
+
+    - name: Install Monero Dependencies
+      shell: bash
+      run: |
+        sudo apt update
+        sudo apt install build-essential libboost-all-dev libsodium-dev
+
+    - name: Install WASM toolchain
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: nightly
+        profile: minimal
+        target: wasm32-unknown-unknown