💄 Hide point markers in generated graphs

[AnandChowdhary]

Summary

• Hides tiny point markers on generated response-time line charts by setting Chart.js v2 point radii to 0
• Replaces the placeholder Jest test with coverage that verifies every rendered graph config disables point markers
• Maintainer-owned replacement for Remove tiny data point circles from prerendered graphs #242; credit to @phieri for the original proposal and investigation

Test plan

• npm test -- --runInBand src/index.spec.ts
• npm run build
• npm test -- --runInBand
• npm pack --dry-run

Supersedes #242.