Add devcontainer configuration

.devcontainer/Dockerfile

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+FROM mcr.microsoft.com/devcontainers/python:3
+
+RUN python -m pip install --upgrade pip \
+    && python -m pip install pytest pytest-cov \
+    && python -m pip install 'flit>=3.8.0'
+
+ENV FLIT_ROOT_INSTALL=1
+
+COPY pyproject.toml README.rst ./
+RUN mkdir -p flit \
+    && python -m flit install --only-deps --deps develop \
+    && rm -r pyproject.toml README.rst flit
+
+// ENV FLIT_ALLOW_INVALID=1
+
+// COPY pyproject.toml .
+// RUN python -m flit install --only-deps --deps develop \
+//     && rm -r pyproject.toml

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.222.0/containers/python-3-miniconda
+{
+	"name": "Python Environment",
+	"build": {
+		"dockerfile": "Dockerfile",
+		"context": ".."
+	},
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"editorconfig.editorconfig",
+				"github.vscode-pull-request-github",
+				"ms-azuretools.vscode-docker",
+				"ms-python.python",
+				"ms-python.vscode-pylance",
+				"ms-python.flake8",
+				"ms-vsliveshare.vsliveshare",
+				"ryanluker.vscode-coverage-gutters",
+				"bungcip.better-toml",
+				"GitHub.copilot"
+			],
+			"settings": {
+				"python.defaultInterpreterPath": "/usr/local/bin/python",
+				"flake8.path": [
+					"/usr/local/py-utils/bin/flake8"
+				]
+			}
+		}
+	}
+}

.vscode/settings.json

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+{
+    "editor.formatOnSave": true,
+    "editor.formatOnPaste": true,
+    "files.trimTrailingWhitespace": true,
+    "files.autoSave": "onFocusChange",
+    "git.autofetch": true,
+    "[jsonc]": {
+        "editor.defaultFormatter": "vscode.json-language-features"
+    },
+    "python.defaultInterpreterPath": "/usr/local/bin/python",
+    "python.formatting.provider": "autopep8",
+    "python.testing.unittestEnabled": false,
+    "python.testing.pytestEnabled": true,
+    "flake8.args": [
+        "--config=.flake8"
+    ],
+    "flake8.path": [
+        "/usr/local/py-utils/bin/flake8"
+    ]
+}