refactor: minor pass through twap imrovements (#2284)

Closes: #XXX

## What is the purpose of the change

Some minor pass through changes discovered while reviewing #2168 
## Documentation and Release Note

  - Does this pull request introduce a new feature or user-facing behavior changes? no
  - Is a relevant changelog entry added to the `Unreleased` section in `CHANGELOG.md`? no
  - How is the feature or change documented? not applicable

x/gamm/twap/keeper.go

@@ -17,11 +17,13 @@ type Keeper struct {
 	ammkeeper types.AmmInterface
 }
 
+const pruneEpochIdentifier = "day"
+
 func NewKeeper(storeKey sdk.StoreKey, transientKey *sdk.TransientStoreKey, paramSpace paramtypes.Subspace, ammKeeper types.AmmInterface) *Keeper {
 	return &Keeper{storeKey: storeKey, transientKey: transientKey, paramSpace: paramSpace, ammkeeper: ammKeeper}
 }
 
 // TODO: make this read from a parameter, or hardcode it.
 func (k *Keeper) PruneEpochIdentifier(ctx sdk.Context) string {
-	return "daily"
+	return pruneEpochIdentifier
 }

x/gamm/twap/store.go

@@ -95,7 +95,7 @@ func (k Keeper) storeNewRecord(ctx sdk.Context, twap types.TwapRecord) {
 // returns the TWAP record from state for (id, t', asset0, asset1),
 // where t' is such that:
 // * t' <= t
-// * there exists no t'' in state, where t'' < t'
+// * there exists no `t'' <= t` in state, where `t' < t''`
 //
 // This returns an error if:
 // * there is no historical record in state at or before t
@@ -140,6 +140,6 @@ func (k Keeper) getRecordAtOrBeforeTime(ctx sdk.Context, poolId uint64, t time.T
 			return twap, nil
 		}
 	}
-	return types.TwapRecord{}, fmt.Errorf("TWAP not found, but there are twaps available for this time."+
+	return types.TwapRecord{}, fmt.Errorf("TWAP not found, but there are other twaps available for this time."+
 		" Were provided asset0denom and asset1denom (%s, %s) correct, and in order (asset0 > asset1)?", asset0Denom, asset1Denom)
 }