Implement Python Dev Environment for `library-python`

[crypto-a]

User Story

As a Python library maintainer,
I need a reproducible dev environment with linting, typing, tests, and CI,
So that contributors can develop and verify changes consistently.

Details and Assumptions

• Use Hatch for envs, builds, and versioning (pyproject.toml).

• Tooling:

  • ruff (lint + format), mypy (typing), pytest + coverage (tests).
  • pre-commit hooks for ruff, mypy (optional), end-of-file-fixer, trailing-whitespace.

• Python support: 3.9–3.12.

• Scripts (via Hatch tool.hatch.envs): lint, fmt, typecheck, test, cov.

• CI: GitHub Actions matrix (3.9–3.12) running hatch run test, ruff, mypy.

• Strict packaging: single source of truth in pyproject.toml (PEP 621 metadata).

Acceptance Criteria

Scenario: Local setup
  Given a clean checkout
  When I run "pipx install hatch" and "hatch env create"
  Then dependencies install successfully for Python 3.9–3.12

Scenario: Code quality gates
  When I run "hatch run lint" and "hatch run typecheck"
  Then ruff reports no errors
  And mypy reports no type issues

Scenario: Test suite
  When I run "hatch run test"
  Then all tests pass
  And coverage summary is printed

Scenario: Pre-commit hooks
  Given pre-commit is installed and configured
  When I commit changes
  Then hooks run ruff formatting and linting
  And commits are blocked on failures

Scenario: CI pipeline
  Given a pull request is opened
  When GitHub Actions runs
  Then lint, typecheck, and tests pass across Python 3.9–3.12