fix x/stats GetStakedAmount and rename to GetStakedBaseTokens (backport #3238)

[mergify]

Changelist

Need to convert delegator shares to tokens to get staked tokens

Test Plan

updated unit test

• failed with original implementation (that didn't have this conversion)
• succeeded with new

Author/Reviewer Checklist

• If this PR has changes that result in a different app state given the same prior state and transaction list, manually add the state-breaking label.
• If the PR has breaking postgres changes to the indexer add the indexer-postgres-breaking label.
• If this PR isn't state-breaking but has changes that modify behavior in PrepareProposal or ProcessProposal, manually add the label proposal-breaking.
• If this PR is one of many that implement a specific feature, manually label them all feature:[feature-name].
• If you wish to for mergify-bot to automatically create a PR to backport your change to a release branch, manually add the label backport/[branch-name].
• Manually add any of the following labels: refactor, chore, bug.

Summary by CodeRabbit

• Refactor
  • Updated staking calculation system to use base token amounts instead of raw staked amounts, improving accuracy of staking-based fee tier discounts and affiliate rewards.
  • Renamed related APIs and types across stats, fee tiers, and affiliates modules for consistency.
  • Added timestamp tracking for cached base token calculations.

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This is an automatic backport of pull request #3238 done by [Mergify](https://mergify.com).

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