NewFromFloat loses precision

See this [example](https://goplay.tools/snippet/WUPyGslBHTi): ``` package main import ( "math/rand/v2" "testing" "github.com/shopspring/decimal" ) func Test(t *testing.T) { // This number is exactly representable as a float64: f64 := float64(rand.Int64()) t.Logf("Number: %f", f64) fromInt := decimal.NewFromInt(int64(f64)) fromFloat := decimal.NewFromFloat(f64) if fromInt.Cmp(fromFloat) != 0 { t.Errorf("from-float (%v) != from-int (%v)", fromFloat, fromInt) } } ``` The above outputs something like: ``` === RUN Test prog_test.go:14: Number: 5202671607238904832.000000 prog_test.go:21: dec2 (5202671607238905000) != original (5202671607238904832) --- FAIL: Test (0.00s) FAIL ``` The original number is 5202671607238904832, but the NewFromFloat-created Decimal is 5202671607238905000.