perf: Deduplicate bech32 encoding in bank send events (#11005)

## Description

performance boost as this is one of the most commonly emitted events





---

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- [ ] added `!` to the type prefix if API or client breaking change
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- [ ] added a changelog entry to `CHANGELOG.md`
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- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
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- [ ] manually tested (if applicable)

x/bank/keeper/send.go

@@ -154,16 +154,18 @@ func (k BaseSendKeeper) SendCoins(ctx sdk.Context, fromAddr sdk.AccAddress, toAd
 		k.ak.SetAccount(ctx, k.ak.NewAccountWithAddress(ctx, toAddr))
 	}
 
+	// bech32 encoding is expensive! Only do it once for fromAddr
+	fromAddrString := fromAddr.String()
 	ctx.EventManager().EmitEvents(sdk.Events{
 		sdk.NewEvent(
 			types.EventTypeTransfer,
 			sdk.NewAttribute(types.AttributeKeyRecipient, toAddr.String()),
-			sdk.NewAttribute(types.AttributeKeySender, fromAddr.String()),
+			sdk.NewAttribute(types.AttributeKeySender, fromAddrString),
 			sdk.NewAttribute(sdk.AttributeKeyAmount, amt.String()),
 		),
 		sdk.NewEvent(
 			sdk.EventTypeMessage,
-			sdk.NewAttribute(types.AttributeKeySender, fromAddr.String()),
+			sdk.NewAttribute(types.AttributeKeySender, fromAddrString),
 		),
 	})