feat: migrated from react 18 to react 19

[ArushKapoorJuspay]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

Upgrades the embedded HyperSwitch Web SDK and demo application to React 19 and ReScript 12.
The changes are limited to build and runtime compatibility. Submit orchestration, postMessage behavior, state architecture, and resource loading are outside this PR.

Changes

• Upgraded React and React DOM to 19.2.8.
• Upgraded ReScript to 12.3.0.
• Upgraded @rescript/react to 0.15.0.
• Added @rescript/runtime 12.3.0.
• Added the ReScript 12 Node requirement.
• Retained classic JSX mode.
• Updated ReScript compiler configuration keys.
• Updated Promise exception normalization for ReScript 12.
• Updated callback-ref handling for React 19.
• Updated the demo to React 19 and @juspay-tech/react-hyper-js 2.3.0.
• Updated CI and release workflows to use a supported Node version and deterministic installation.
• Preserved existing Jotai Provider isolation.
• Restored unrelated lockfile changes to minimize the patch.

Compatibility

The following behavior remains unchanged:

• window.Hyper
• window.Hyper.init
• Conditional window.Stripe
• removeBeforeUnloadEventListeners
• loadHyper and deprecated loadStripe
• WordPress-specific loader behavior
• v1 and v2 SDK APIs
• Existing Promise exception identity and wrapping behavior

Validation

• npm ci --ignore-scripts
• npm run re:clean && npm run re:build
• npm run build
• npm run build:v2
• npm run test:hooks
• Demo npm ci --ignore-scripts
• Demo npm run build
• Demo npm run build:v2
• Dependency-tree validation with npm ls
• Focused Promise rejection checks for null, undefined, JavaScript errors, JsExn, and ReScript exceptions
• git diff --cached --check

How did you test it?

Checklist

• I ran npm run re:build
• I reviewed submitted code
• I added unit tests for my changes where possible

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
.github/workflows/run-automation-test.yml	98% smaller
package.json	51% smaller
Hyperswitch-React-Demo-App/package-lock.json	41% smaller
Hyperswitch-React-Demo-App/package.json	32% smaller
rescript.json	20% smaller
package-lock.json	20% smaller
.github/workflows/stable-release.yml	0% smaller
.gitignore	Unsupported file format
README.md	Unsupported file format
src/Components/PortalCapture.res	Unsupported file format
src/libraries/Promise.res	Unsupported file format
src/libraries/Promise.resi	Unsupported file format

[github-actions]

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[XyneSpaces]

[blocking] This React 19/ReScript 12 migration needs to be consolidated with #1712 before merge. Both PRs modify the same migration surface (package.json, lockfiles, rescript.json, PortalCapture.res, and Promise.res) with conflicting dependency/config choices, so merging one first will leave the other resolving conflicts by overwriting migration code rather than reviewing a single coherent upgrade.