feat: add auto lint fix tooling with isort and enhanced pre-commit

[Ayush10]

Summary

• Adds isort for automatic import sorting (black-compatible profile, line length 120)
• Enhances .pre-commit-config.yaml with additional hooks:
  • trailing-whitespace, end-of-file-fixer, check-yaml, debug-statements, check-added-large-files
  • isort hook for automatic import sorting on commit
  • Fixed black hook to use proper arg format and exclude _version.py
• Adds make fix target for one-command auto-formatting (black + isort + nbqa)
• Adds make isort check target and includes it in make lint
• Adds isort check step to CI workflow (test_qlib_from_source.yml)
• Configures [tool.isort] and [tool.black] in pyproject.toml
• Applies initial import sorting across all 177 Python files (mechanical, auto-generated)

Changes breakdown

Commit	Description	Files
1st	Add tooling config (pre-commit, Makefile, pyproject.toml, CI)	4
2nd	Auto-fix import sorting via isort qlib scripts	177

How developers use this

# Auto-fix all formatting issues (black + isort + nbqa)
make fix

# Check only (used in CI)
make lint    # includes: black, isort, pylint, flake8, mypy, nbqa

# Pre-commit hooks run automatically on git commit
pre-commit install

Test plan

• isort --check-only qlib scripts passes after fix
• Key imports verified: qlib.config, qlib.data.ops, qlib.contrib.strategy
• All import changes are mechanical (no logic modifications)
• Existing tests pass without modification

Closes #2060