net: Don't use checked arithmetic when parsing numbers with known max digits Add a branch to `Parser::read_number` that determines whether checked or regular arithmetic is used. - If `max_digits.is_some()`, then we know we are parsing a `u8` or `u16` because `read_number` is only called with `Some(3)` or `Some(4)`. Both types fit within a `u32` without risk of overflow. Thus, we can use plain arithmetic to avoid extra instructions from `checked_mul` and `checked_add`. Add benches for `IpAddr`, `Ipv4Addr`, `Ipv6Addr`, `SocketAddr`, `SocketAddrV4`, and `SocketAddrV6` parsing