perf: Remove an extra heap allocation from NewLegacyDec (#19466)

Co-authored-by: Marko <marbar3778@yahoo.com>

Author: ValarDragon

math/CHANGELOG.md

@@ -43,6 +43,7 @@ Ref: https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.j
 
 * [#18874](https://github.com/cosmos/cosmos-sdk/pull/18874) Speedup `math.Int.Mul` by removing a duplicate overflow check
 * [#19386](https://github.com/cosmos/cosmos-sdk/pull/19386) Speedup `math.Int` overflow checks
+* [#19466](https://github.com/cosmos/cosmos-sdk/pull/19466) Speedup `math.NewLegacyDec` by one heap allocation
 * [#19467](https://github.com/cosmos/cosmos-sdk/pull/19467) Slightly speedup `math.LegacyDec` `Ceil` and `MarshalTo` methods
 
 ### Bug Fixes

math/dec.go

@@ -102,8 +102,9 @@ func LegacyNewDec(i int64) LegacyDec {
 // create a new Dec from integer with decimal place at prec
 // CONTRACT: prec <= Precision
 func LegacyNewDecWithPrec(i, prec int64) LegacyDec {
+	bi := big.NewInt(i)
 	return LegacyDec{
-		new(big.Int).Mul(big.NewInt(i), precisionMultiplier(prec)),
+		bi.Mul(bi, precisionMultiplier(prec)),
 	}
 }