chore: update dependencies and modernize tooling

[devCrossNet]

What is accomplished by your PR?

Update all dependencies and replace outdated tooling (last update: 2021).

• Replace Jest 27 + ts-jest with Vitest 5
• Migrate ESLint 7 to ESLint 10 flat config with typescript-eslint 8
• Update TypeScript 4.4 → 6.0, Prettier 2 → 3, Husky 7 → 9, commitlint, np, rimraf
• Replace deprecated lodash.get with internal getByPath helper (no runtime dependencies anymore)
• Remove postinstall: husky install, which ran for package consumers
• Add typecheck script and engines.node >=22
• Add GitHub Actions CI (Node 22 + 24): typecheck, test, lint, prettier check, build

Is there something controversial in your PR?

• Coverage thresholds for lines/statements lowered to 99, because V8 counts differently than Istanbul. Same 2 uncovered lines as before.
• TypeScript stays on 6.0, because typescript-eslint does not support TS 7 yet.
• npm audit shows 6 high findings, all from np → braces (dev-only release tool, no fix available yet).

Checklist

• Run unit tests to ensure all existing tests are still passing
• Add new passing unit tests to cover the code introduced by your PR
• Change documentation for the code introduced by your PR

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