isNumber function
Returns true if input is a base-10 integer (surrounding whitespace is
trimmed first). Parsing is pinned to radix: 10, so the 0x hex prefix,
scientific notation and decimals are all rejected — use isDecimal for
fractional values.
Implementation
bool isNumber(String? input) =>
int.tryParse(input?.trim() ?? '', radix: 10) != null;