fix: resolve 4 bugs in termui

[saurabhhhcodes]

Description

This PR fixes real bugs found in the codebase:

• Simplified empty-string validation: comparing trim() to '' misses whitespace-only input; .trim().length === 0 is explicit.
• Replaced global isNaN with Number.isNaN: the global version coerces its argument, so isNaN('1') returns false while Number.isNaN is strict.
• Simplified empty-string validation: comparing trim() to '' misses whitespace-only input; .trim().length === 0 is explicit.
• Added Number.EPSILON to Math.round: prevents floating-point drift (e.g. 1.005 * 100 rounding to 100 instead of 101).

Type of Change

• Bug fix (non-breaking change fixing an issue)

How Has This Been Tested?

• Local manual testing

Checklist

• My code follows the style guidelines
• I have performed a self-review

Related Issue

Ref: #3462

Summary by CodeRabbit

• Bug Fixes
  • Improved calculator validation for negative number inputs.
  • Improved FPS display accuracy by reducing rounding-related inconsistencies.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d653fd48-d471-41fc-ac13-959bd37e08db

📥 Commits

Reviewing files that changed from the base of the PR and between 6c7584e and 7fc4ca4.

📒 Files selected for processing (2)

• examples/calculator/src/index.tsx
• packages/dev-server/src/devtools.ts

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📝 Walkthrough

Walkthrough

The change replaces global numeric validation in the calculator and adjusts FPS rounding in the development server with Number.EPSILON.

Changes

Calculator validation

Layer / File(s)	Summary
Strict negative-number validation examples/calculator/src/index.tsx	safeEval uses Number.isNaN to validate the initial negative-number token.

FPS rounding

Layer / File(s)	Summary
FPS precision adjustment packages/dev-server/src/devtools.ts	recordRender adds Number.EPSILON before rounding FPS to one decimal place.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Karanjot786/TermUI#3367: Replaces global isNaN with Number.isNaN in the same calculator validation code.
• Karanjot786/TermUI#3413: Makes the same Number.EPSILON FPS-rounding change.
• Karanjot786/TermUI#3453: Updates DevTools.recordRender with the same FPS rounding adjustment.

Suggested reviewers: karanjot786

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the fixes and testing, but it omits required package, GSSoC, screenshots, notes, and checklist details and does not use the required Closes # format.	Complete every template section, identify the affected packages, use Closes #3462``, and update all applicable checklist and GSSoC fields.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies a bug-fix change and follows the required type prefix format.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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