Upgraded babel to v8

[david-yz-liu]

Proposed Changes

(Describe your changes here. Also describe the motivation for your changes: what problem do they solve, or how do they improve the application or codebase? If this pull request fixes an open issue, use a keyword to link this pull request to the issue.)

Upgrades Babel from v7 to v8 (@babel/core, preset-env, preset-react), along with babel-loader and babel-jest to the first patch versions that declare Babel 8 peer support.

Babel 8 removed several options this repo relied on directly, so babel.config.js needed matching changes:

• useBuiltIns/corejs were removed from preset-env and replaced with babel-plugin-polyfill-corejs3
• The regenerator option on plugin-transform-runtime was removed. Replaced with babel-plugin-polyfill-regenerator
• The helpers option on plugin-transform-runtime was removed; since this repo already ran helpers: false, the plugin — along with the now-unused @babel/plugin-transform-runtime and @babel/runtime deps — was dropped entirely, per Babel's own migration guidance for that case.
• preset-react's JSX runtime default flipped from classic to automatic in v8; pinned runtime: "classic" explicitly to keep this a no-behavior-change dependency bump. Switching to automatic (and dropping now-unnecessary import React from "react" lines) is left for a follow-up PR.
• Added regenerator-runtime as a direct dependency since it's now imported straight into the shipped bundle instead of coming in via @babel/runtime.

Screenshots of your changes (if applicable)

Type of Change

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Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)	X
📖 Documentation update (change that updates documentation)
🔧 Internal (change that only affects developers or continuous integration)

Checklist

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[coveralls]

Coverage Report for CI Build 28677331602

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage remained the same at 90.274%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	51018
Covered Lines:	47070
Line Coverage:	92.26%
Relevant Branches:	2435
Covered Branches:	1184
Branch Coverage:	48.62%
Branches in Coverage %:	Yes
Coverage Strength:	127.13 hits per line

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💛 - Coveralls