Fix flaky test: ESM module loading race condition in test_subcomponent_notation

[Copilot]

Description

Tests test_subcomponent_notation_as_str_attrs and test_subcomponent_notation_as_obj_attrs were failing intermittently with Cannot read properties of null (reading 'useContext'). The issue was a race condition where react-bootstrap attempted to access React's context API before its peer dependencies were fully initialized in the ESM module graph.

Fix:

• Pin esm.sh to version 135 for deterministic CDN builds
• Explicitly import react-is before react-bootstrap to ensure proper module loading order
• Add comments documenting why the import is necessary

import React from "https://esm.sh/v135/react@19.0"
import ReactDOM from "https://esm.sh/v135/react-dom@19.0/client"
// Explicitly import react-is to ensure it's loaded before react-bootstrap
// This prevents race conditions where react-bootstrap tries to use React context before deps are ready
import * as ReactIs from "https://esm.sh/v135/react-is@19.0"
import {InputGroup, Form} from "https://esm.sh/v135/react-bootstrap@2.10.2?deps=react@19.0,react-dom@19.0,react-is@19.0&exports=InputGroup,Form";

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

_{By submitting this pull request I agree that all contributions comply with this project's open source license(s).}

Original prompt

Reference: https://github.com/reactive-python/reactpy/actions/runs/20151411474/job/57844821678

Determine the cause of this flaky failure and implement a solution.

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