test(tooltipUtils): add timezone normalization and calendar boundary tests

[aanyacloud]

Description

Adds timezone boundary test coverage for tooltipUtils to verify date normalization and calendar boundary alignment.

Fixes #2640

Pillar

• 🟡 Pillar 1 — New Theme Design
• 🔷 Pillar 2 — Geometric SVG Improvement
• ⚪ Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

N/A (Test-only changes)

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally.
• I have run npm run format and npm run lint locally and resolved all errors.
• My commits follow the Conventional Commits format.
• I have updated README.md if I added a new theme or URL parameter.
• I have starred the repo.
• I have made sure that I have only one commit to merge in this PR.
• The changes are limited to test coverage and do not affect application behavior.
• (Recommended) I joined the CommitPulse Discord community.

[vercel]

@aanyacloud is attempting to deploy a commit to the jhasourav07's projects Team on Vercel.

A member of the Team first needs to authorize it.