don't use core::error for compiler compatibility

src/calc.rs

@@ -1,4 +1,4 @@
-use core::{convert::Infallible, error::Error, fmt::Display};
+use core::{convert::Infallible, fmt::Display};
 
 use num_traits::{PrimInt, Unsigned};
 
@@ -11,7 +11,6 @@ pub enum StackCalcError {
     DecimalError(DecimalError),
 }
 
-impl Error for StackCalcError {}
 impl Display for StackCalcError {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {

src/lib.rs

@@ -2,7 +2,7 @@
 
 pub mod calc;
 
-use core::{error::Error, fmt::Display};
+use core::fmt::Display;
 #[cfg(not(test))]
 use num_traits::float::FloatCore;
 use num_traits::{one, zero, PrimInt, Unsigned};
@@ -13,7 +13,6 @@ pub enum DecimalError {
     NotANumber,
 }
 
-impl Error for DecimalError {}
 impl Display for DecimalError {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {