refactor: deepen store selection module

[okyrychenko-dev]

Summary

Concentrate Store selection behavior within the existing Store selection module, improving locality without changing consumer-visible behavior or public type contracts.

Changes

• Keep Store selection bindings as the single interface used by Global, Provider, and Resolved stores.
• Organize retained selection, equality caching, identity selection, and plain selection into private hooks, utilities, and types within the Store selection module.
• Remove the standalone equality-selector module and its internal exports.
• Remove the generic identity-selector utility interface while retaining identity behavior as a private Store selection utility.
• Preserve directory barrel imports, selector overloads, middleware types, and existing runtime behavior.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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