Update rust/qrcode example

* bump up `dfx` version
* bump up `candid` version
* autoformat files
* `cargo update`
* `npm update`
* `cargo clippy`
* add tests
* add GitHub workflow
* add `rust-toolchain.toml`

Author: berestovskyy

.github/workflows/rust-qrcode-example.yaml

@@ -0,0 +1,39 @@
+name: rust-qrcode
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    paths:
+      - rust/qrcode/**
+      - .github/workflows/provision-darwin.sh
+      - .github/workflows/provision-linux.sh
+      - .github/workflows/rust-qrcode-example.yaml
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+jobs:
+  rust-qrcode-example-darwin:
+    runs-on: macos-12
+    steps:
+      - uses: actions/checkout@v1
+      - name: Provision Darwin
+        run: DFX_VERSION="0.15.2" bash .github/workflows/provision-darwin.sh
+      - name: Rust QRCode Darwin
+        run: |
+          dfx start --background
+          pushd rust/qrcode
+          make test
+          popd
+  rust-qrcode-example-linux:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v1
+      - name: Provision Linux
+        run: DFX_VERSION="0.15.2" bash .github/workflows/provision-linux.sh
+      - name: Rust QRCode Linux
+        run: |
+          dfx start --background
+          pushd rust/qrcode
+          make test
+          popd

.github/workflows/rust-qrcode-skip.yaml

@@ -0,0 +1,20 @@
+name: rust-qrcode
+on:
+  pull_request:
+    paths-ignore:
+      - rust/qrcode/**
+      - .github/workflows/provision-darwin.sh
+      - .github/workflows/provision-linux.sh
+      - .github/workflows/rust-qrcode-example.yaml
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+jobs:
+  rust-qrcode-example-darwin:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo 'Not needed - relevant folder not touched'
+  rust-qrcode-example-linux:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo 'Not needed - relevant folder not touched'