Replace pylint with ruff

[janhoy]

This just replaces the tool and fixes some linting issues.

Closes #6

(In another PR we'll enforce source formatting with ruff as well.)

[Copilot]

Pull request overview

This PR replaces the project’s Python linting toolchain from pylint to ruff, updates developer/CI entry points to use ruff check, and includes a handful of small code cleanups to satisfy the new lint rules/config.

Changes:

• Remove pylint configuration and dependency; add ruff configuration under [tool.ruff] in pyproject.toml.
• Update make lint (and developer docs) to run ruff check ..
• Apply small lint-driven fixes across the codebase (import splitting, not in style, remove unused import/exception binding, whitespace cleanup).

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/unit/solr/test_client.py	Split multi-import statements to satisfy linting style.
solrorbit/workload/params.py	Use idiomatic not in membership checks.
solrorbit/workload/loader.py	Use idiomatic not in membership checks.
solrorbit/worker_coordinator/worker_coordinator.py	Remove unused exception binding in a JSON parsing except.
solrorbit/metrics.py	Remove an unused stdlib import (time).
scripts/expand-data-corpus.py	Fix indentation/whitespace in an argparse help string literal block.
pyproject.toml	Replace pylint with ruff dependency and add ruff configuration.
Makefile	Switch lint target from pylint to ruff check ..
AGENTS.md	Update developer guidance to reference ruff instead of pylint.
.pylintrc	Remove pylint configuration file.
.ci/scripts/check_deprecated_terms.py	Split multi-import statement to satisfy linting style.

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