Remove dead [tool.black] config from pyproject.toml

[turbomam]

Context

PR #492 migrated tox.ini [testenv:format] from black to ruff format, and pre-commit already uses ruff-format. The repo is now fully using ruff for formatting.

However, pyproject.toml still has a [tool.black] section (line 73):

[tool.black]
line-length = 100
target-version = ["py38", "py39", "py310"]

This is dead config — nothing invokes black anymore.

Action

• Remove the [tool.black] section from pyproject.toml
• Verify [tool.ruff.format] has equivalent settings (line-length is already set to 100 under [tool.ruff])
• Update target Python versions while at it — py38 and py39 are EOL

Ref: #492