Allow bounded numbers to be deserialized from strings

[DrChat]

Fixes #295.

This allows bounded integers to be deserialized from strings.
The specific implementation comes from serde-rs/json#412.

Note: The diff is a bit of a mess because I had to indent everything.
This is the specific code that was added (for all three types):

            impl<'de, const MAX: $primitive> Deserialize<'de> for $lim<MAX> {
                fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
                    where D: serde::Deserializer<'de>
                {
                    struct Visitor<const MAX: $primitive>;

                    impl<'de, const MAX: $primitive> serde::de::Visitor<'de> for Visitor<MAX> {
                        type Value = $lim<MAX>;

                        fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                            f.write_str("integer as a number or string")
                        }

                        fn [<visit_ $primitive>]<E>(self, val: $primitive) -> Result<Self::Value, E>
                            where E: serde::de::Error
                        {
                            $lim::new(val).map_err(serde::de::Error::custom)
                        }

                        fn visit_str<E>(self, val: &str) -> Result<Self::Value, E>
                            where E: serde::de::Error
                        {
                            let v = val.parse().map_err(serde::de::Error::custom)?;
                            $lim::new(v).map_err(serde::de::Error::custom)
                        }
                    }

                    deserializer.deserialize_any(Visitor)
                }
            }

[sugyan]

I didn't know that this kind of conversion is possible.
But I don't understand why it is necessary to deserialize from string to integer. Can you tell me in what specific cases this is necessary?

[sugyan]

Oh... sorry, I didn't read the #295 one. I see, so you are saying that this kind of conversion is necessary when HTTP query parameters are received, etc.

[DrChat]

All good! And yup - axum will treat all query parameters as strings when performing deserialization, so we'd have to handle that here in order to be compatible.

I'm also open to other ways to implement this too - this just seemed to be the best way to do it based on what I saw :)