Remove tslib runtime dep / enable coverage report / bump node to 18

[huntharo]

• Remove need for tslib at runtime, by this library (granted AWS SDK still needs it)
• Add coverage report for PR builds
• Update dependencies
• Bump from node 16 to 18

[github-actions]

📊 Node.js Code Coverage Report

File	Lines	Lines Hit / Found	Uncovered Lines	Branches
src/deep-replace-dates-with-strings.ts	✅ 100.0%	22 / 22	0	100.0%
src/dynamodb-store.ts	✅ 93.5%	571 / 611	40	72.3%
Overall	✅ 93.7%	593 / 633	40	76.8%