🔧 (dev-check.sh, pyproject.toml, requirements.txt): add development tooling and configuration

Introduce a dev-check.sh script to automate code formatting and import
sorting using Black and isort. Add a pyproject.toml file to configure
Black and isort settings for consistent code style. Update
requirements.txt to include Black and isort as development dependencies
and remove version pinning for easier dependency management.

These changes streamline the development workflow, enforce code style
consistency, and make it easier for contributors to run formatting and
import checks locally.

pyproject.toml

@@ -0,0 +1,24 @@
+[tool.black]
+line-length = 160
+target-version = ['py38']
+include = '\.pyi?$'
+extend-exclude = '''
+/(
+  \.eggs
+  | \.git
+  | \.hg
+  | \.mypy_cache
+  | \.tox
+  | \.venv
+  | build
+  | dist
+)/
+'''
+
+[tool.isort]
+line_length = 160
+multi_line_output = 3
+include_trailing_comma = true
+force_grid_wrap = 0
+use_parentheses = true
+ensure_newline_before_comments = true