[MAINTENANCE] Remove ability to configure store names

[cdkini]

Remove _store_name top level variables to prevent user configuration (deemed unnecessary). Utilize a new StoreManager abstraction to add helpful error messaging and better access around stores

• [x] Description of PR changes above includes a link to an existing GitHub issue
• [x] PR title is prefixed with one of: [BUGFIX], [FEATURE], [DOCS], [MAINTENANCE], [CONTRIB]
• [x] Code is linted - run invoke lint (uses ruff format + ruff check)
• [x] Appropriate tests and docs have been updated

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