Add async epic helper

[apples-kksk]

Closes #162.

Adds createAsyncEpic, a redux-observable-compatible helper for async action objects. It listens for request actions, runs a typed handler, maps emitted values to success actions, maps errors to failure actions, and cancels active work when an optional cancel action is emitted.

Notes:

• Uses RxJS types for the public epic shape, but avoids runtime top-level RxJS imports in the bundled package.
• Adds tests for success, promise completion, error mapping, custom mapError, cancellation, and type inference.
• Documents usage in the redux-observable tutorial and API section.

Verification:

• npm run ci-check
• NODE_OPTIONS=--openssl-legacy-provider npm run build
• git diff --check

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #162: Add a generic redux-observable factory automatically handling async-actions - createAsyncEpic

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[gemini-code-assist]

Code Review

This pull request introduces the createAsyncEpic helper, which simplifies the creation of redux-observable epics by automatically handling the request, success, failure, and cancellation lifecycle of async actions. The implementation includes new tests, documentation, and updates to dependencies. Review feedback highlights opportunities to improve compatibility with environments lacking Symbol support, optimize iteration logic when observers are closed, and enhance type safety for error mapping. It is also recommended to explicitly document the 'switch' strategy behavior used for managing concurrent requests.