Add config/18.0/ with configuration files based on OCA standards:
- .pylintrc and .pylintrc-mandatory (valid-odoo-versions=18.0)
- .ruff.toml (Python linting)
- .pre-commit-config.yaml with updated hooks:
- whool-init (new in 18.0)
- oca-gen-external-dependencies (new in 18.0)
- Updated prettier 3.x and eslint 9.x
- eslint.config.cjs and prettier.config.cjs (new flat config format)
Also move .eslintrc.yml and .prettierrc.yml to config/16.0/ since
18.0 uses the new CJS flat config format instead of YAML.
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