Add ruff, black, and mypy checks to CI

[srichs]

Motivation

• Ensure consistent code quality and static analysis by running ruff, black --check, and mypy during CI.

Description

• Added a lint job to .github/workflows/ci.yml that runs on ubuntu-latest with Python 3.11 and executes pip install -e .[lint], ruff check ., black --check ., and mypy spot_api.
• Updated pyproject.toml to include black>=24.0 in the [project.optional-dependencies].lint group alongside mypy and ruff so the CI job can install all lint tools via .[lint].

Testing

• Attempted to run python -m pip install --upgrade pip && pip install -e .[lint] && ruff check . && black --check . && mypy spot_api locally, but the dependency installation failed due to network/proxy restrictions, so lint checks could not be executed in this environment (installation failed).
• Existing tests and docs CI jobs were left unchanged and continue to run as before.

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Codex Task