chore: upgrade ESLint

[hakanson]

Issue #, if available: #196

Description of changes:

Updated actions/checkout to v4, actions/setup-node to v4, and node-version to 18 in workflows

Update to ESLint 9.x (v8 is EOL per https://eslint.org/version-support/)

• updated related eslint packages and upgrade eslint-plugin-security
• ran npx @eslint/migrate-config .eslintrc.js per Configuration Migration Guide to create eslint.config.mjs
• --ignore-path .gitignore on command line replaced with setting in eslint.config.mjs
• set @typescript-eslint/no-require-imports to "off" in some test files
• removed unused eslint-disable-next-line

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[hakanson]

Looks like structuredClone used by ESLint security plugin was introduced in Node.js 17.0.0 and we run on 16. Created #196 and updating workflows.