chore(deps): upgrade react 19 and rescript 12

[LakSHyaMudgal1]

Closes #1711

Summary

This PR upgrades the HyperSwitch Web SDK build stack to React 19 and ReScript 12 while preserving existing SDK behavior and merchant-facing APIs.

Changes

• Upgrade React and ReactDOM to React 19
• Upgrade ReScript to 12.3.0
• Upgrade @rescript/react to 0.15.0
• Add @rescript/runtime 12.3.0
• Remove deprecated -bs-super-errors compiler flag
• Update Promise exception handling for ReScript 12 compatibility
• Update callback refs for React 19 compatibility

Testing

• ReScript compilation succeeds
• Production build succeeds
• Demo app builds successfully
• ESLint passes
• Dependency tree verified using npm ls

Notes

This change preserves existing merchant-facing APIs and maintains compatibility for both v1 and v2 SDKs.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
package.json	53% smaller
Hyperswitch-React-Demo-App/package.json	31% smaller
Hyperswitch-React-Demo-App/package-lock.json	27% smaller
rescript.json	20% smaller
package-lock.json	19% smaller
.gitignore	Unsupported file format
src/Components/PortalCapture.res	Unsupported file format
src/libraries/Promise.res	Unsupported file format
src/libraries/Promise.resi	Unsupported file format

[XyneSpaces]

[blocking] This React 19/ReScript 12 migration needs to be consolidated with #1710 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.

[LakSHyaMudgal1]

[blocking] This React 19/ReScript 12 migration needs to be consolidated with #1710 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.

I have consolidated the dependency versions (react 19.2.8), rescript.json key migrations (compiler-flags, dependencies), and Promise.res / Promise.resi exception handling from PR #1710 into PR #1712. ReScript 12 build completes cleanly with zero configuration deprecation warnings.