Add Dev Container (#8)

This PR adds a [Dev Container](https://containers.dev) to the project
for easier project setup and development.

There are a number of IDEs and tools that support Dev Containers, but
the following testing instructions will assume VS Code (for good or for
ill).


0. Install Docker Desktop, VS Code, and the VS Code Dev Containers
extension
1. Switch to this branch: `git switch add-devcontainer`
2. Open the project in VS Code
3. Open the command palette (`cmd-shift-p` on macOS) and serach for "Dev
Containers: Reopen in Container"
4. Wait for the Dev Container to pull and build the development image
5. Open a new VS Code terminal tab (`cmd-j` on macOS to show the panel)
6. Run formatting: `mix format --check-formatted`
7. Run tests: `mix test`
8. Generate docs: `mix docs`

🥳

.devcontainer/devcontainer.json

@@ -0,0 +1,37 @@
+// For format details, see https://aka.ms/devcontainer.json.
+{
+    "name": "compare_chain",
+    // Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+    "image": "elixir:1.16-otp-26-slim",
+
+    // Features to add to the dev container. More info: https://containers.dev/features.
+    "features": {
+      "ghcr.io/devcontainers/features/common-utils:2": {
+        "installOhMyZsh": false,
+        "installOhMyZshConfig": false
+      },
+      "ghcr.io/devcontainers/features/git:1": {
+        "version": "latest"
+      },
+      "ghcr.io/devcontainers/features/github-cli:1": {}
+    },
+
+    // Use 'forwardPorts' to make a list of ports inside the container available locally.
+    // "forwardPorts": [],
+
+    // Use 'postCreateCommand' to run commands after the container is created.
+    "postCreateCommand": ".devcontainer/setup.sh",
+
+    // Configure tool-specific properties.
+    "customizations": {
+        "vscode": {
+            "extensions": [
+              "EditorConfig.EditorConfig",
+              "JakeBecker.elixir-ls"
+            ]
+        }
+    }
+
+    // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+    // "remoteUser": "root"
+}

.devcontainer/setup.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+mix local.hex --force
+mix deps.get

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_size = 2
+indent_style = space
+trim_trailing_whitespace = true

.gitignore

@@ -24,3 +24,6 @@ compare_chain-*.tar
 
 # Temporary files, for example, from tests.
 /tmp/
+
+# Ignore files generated by Elixir Language Server IDE plugin.
+.elixir_ls