fix(alchemy-signer): check if process is defined before reading env vars

[Dan-Nolan]

Pull Request Checklist

• Did you add new tests and confirm existing tests pass? (yarn test)
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PR-Codex overview

This PR updates the way the ROOT_ORG_ID is determined in the signer/client/index.ts file to handle different environments more effectively.

Detailed summary

• Introduced _ENV_ROOT_ORG_ID to handle environment checks
• Updated ROOT_ORG_ID assignment to use _ENV_ROOT_ORG_ID or default value

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