Cache updatecache fix

[MudDev]

This pull request simplifies the logic for enabling the TopHolders module and improves compatibility for nodes that enable the module after initial setup. It removes the distinction between fresh and existing nodes, ensuring the store key is always added when TopHolders is enabled, and updates the upgrade handler to automatically add the store if needed. Additionally, it fixes a timestamp issue in the TopHolders cache.

TopHolders module improvements:

• Simplified TopHolders store key logic: The conditional check for fresh vs. existing nodes is removed; the store key is always appended to storeKeys when TopHolders is enabled, making the initialization consistent and easier to maintain (evmd/app.go).
• Unified TopHolders keeper initialization: The keeper is now always initialized with the store key, removing unnecessary checks and supporting backward compatibility more cleanly (evmd/app.go).

Upgrade handling enhancements:

• Automatic TopHolders store addition: The upgrade handler now ensures the TopHolders store is added if the module is enabled, even for nodes that enable it after passing the upgrade height, simplifying operational complexity (evmd/upgrades.go).

Bug fix:

• Correct cache timestamp: The TopHolders cache now uses the block time from sdkCtx instead of the current system time, ensuring accurate and deterministic timestamps (x/topholders/keeper/cache.go).

Cleanup:

• Removed unused filepath import from evmd/app.go, reflecting the simplified initialization logic.