feat: prepare for initial release

Includes code from all commits in internal repo up to 6a7b313

Prepared in the following way:

```
git fetch github main
git checkout -b prepare-0.1.0 github/main  
git merge --squash 6a7b313
```

.flake8

@@ -0,0 +1,35 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Generated by synthtool. DO NOT EDIT!
+[flake8]
+ignore = E203, E231, E266, E501, W503
+exclude =
+  third_party/**
+
+  # Exclude generated code.
+  **/proto/**
+  **/gapic/**
+  **/services/**
+  **/types/**
+  *_pb2.py
+
+  # Standard linting exemptions.
+  **/.nox/**
+  __pycache__,
+  .git,
+  *.pyc,
+  conf.py

.gitignore

@@ -0,0 +1,70 @@
+*.py[cod]
+*.sw[op]
+
+# C extensions
+*.so
+
+# Packages
+*.egg
+*.egg-info
+dist
+build
+eggs
+.eggs
+parts
+bin
+var
+sdist
+develop-eggs
+.installed.cfg
+lib
+lib64
+__pycache__
+
+# Installer logs
+pip-log.txt
+
+# Unit test / coverage reports
+.coverage
+.coverage.*
+.nox
+.cache
+.mypy_cache
+.pytest_cache
+.pytype
+
+
+# Mac
+.DS_Store
+
+# JetBrains
+.idea
+
+# VS Code
+.vscode
+
+# emacs
+*~
+
+# Built documentation
+docs/_build
+bigquery/docs/generated
+docs.metadata
+
+# Virtual environment
+env/
+venv/
+
+# Test logs
+coverage.xml
+*sponge_log.xml
+
+# System test environment variables.
+system_tests/local_test_setup
+
+# Make sure a generated file isn't accidentally committed.
+pylintrc
+pylintrc.test
+
+# Notebook scratch
+.ipynb_checkpoints

.isort.cfg

@@ -0,0 +1,7 @@
+[settings]
+profile=black
+force_sort_within_sections=True
+lexicographical=True
+single_line_exclusions=('typing',)
+order_by_type=False
+group_by_package=True

.kokoro/build.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+if [[ -z "${PROJECT_ROOT:-}" ]]; then
+    PROJECT_ROOT="${KOKORO_ARTIFACTS_DIR}/git/bigframes"
+fi
+
+cd "${PROJECT_ROOT}"
+
+# Disable buffering, so that the logs stream through.
+export PYTHONUNBUFFERED=1
+
+# Debug: show build environment
+env | grep KOKORO
+
+# Install pip
+python3 -m pip install --upgrade --quiet pip
+python3 -m pip --version
+
+# Remove old nox
+python3 -m pip uninstall --yes --quiet nox-automation
+
+# Install nox
+python3 -m pip install --upgrade --quiet nox
+python3 -m nox --version
+
+# If NOX_SESSION is set, it only runs the specified session,
+# otherwise run all the sessions.
+if [[ -n "${NOX_SESSION:-}" ]]; then
+    python3 -m nox --stop-on-first-error -s ${NOX_SESSION:-}
+else
+    python3 -m nox --stop-on-first-error
+fi

.kokoro/continuous/common.cfg

@@ -0,0 +1,10 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+build_file: "bigframes/.kokoro/build.sh"

.kokoro/continuous/continuous.cfg

@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto

.kokoro/continuous/e2e.cfg

@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "system_prerelease system_noextras e2e notebook samples"
+}

.kokoro/continuous/nightly.cfg

@@ -0,0 +1,8 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "NOX_SESSION"
+    value: "unit unit_prerelease system system_prerelease cover lint lint_setup_py mypy format docs e2e notebook"
+}
+
+build_file: "bigframes/.kokoro/release-nightly.sh"

.kokoro/presubmit/common.cfg

@@ -0,0 +1,10 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+build_file: "bigframes/.kokoro/build.sh"

.kokoro/presubmit/e2e.cfg

@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "system_prerelease system_noextras e2e notebook samples"
+}

.kokoro/presubmit/presubmit.cfg

@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto