[SCAL-216889] improve test coverage for ts-chart-sdk

[abey-thomas]

Previous coverage:

New coverage:

[github-actions]

File	Coverage
All files	89%	✅
src/main/custom-chart-context.ts	86%	✅
src/main/post-message-event-bridge.ts	81%	✅
src/main/util.ts	75%	✅
src/react/use-custom-chart-context.tsx	86%	✅
src/react/mocks/custom-chart-context-mock.ts	96%	✅
src/utils/conditional-formatting/conditional-formatting.ts	92%	✅

Minimum allowed coverage is 0%

Generated by 🐒 cobertura-action against f060f2c