Fix compilation errors for embedded platforms like Xtensa/ESP32

[hwmaier]

serde_valid is a very useful add-on for serde deserializations.

This PR contains changes to compile it for embedded platforms which don't autodetect std feature and i128 feature. Specifically the ESP32 platform.

To compile there, indexmap needs feature std enabled. In addition num_traits won't have the traits for i128 enabled, so this PR makes the numeric_multiple_of validations for 128-bit integers only available if the i128 feature is enabled and avoids a compilation error if not.

[hwmaier]

Alternatively to adding #[cfg(feature = "num-traits/i128")] it may be better to add the i128 feature to the num_traits package in Cargo.toml:

num-traits = { version = "^0.2", features = ["i128"] } 

[yassun7010]

Thanks for the PR.

I prefer to add "#[cfg(feature = "num-traits/i128")]".

I will release it as soon as possible after you fix it!

[hwmaier]

I prefer to add "#[cfg(feature = "num-traits/i128")]".

I will release it as soon as possible after you fix it!

Hi @yassun4dev, I reverted my last commit to use your preferred #[cfg(feature = "num-traits/i128")] solution.

[yassun7010]

@hwmaier I released v0.15.0.

I found that some of my applications that use i128 fail to compile, so I ended up adding the i128 feature.

For backward compatibility, the i128 feature is supported by default, and can be used without editing the settings in Cargo.toml.

[hwmaier]

I found that some of my applications that use i128 fail to compile, so I ended up adding the i128 feature.

Great. I checked the latest v0.15.0 release today and compiled it for the embedded ESP32 platform and all compiles without error out of the box.

Thank you so much for incorporating these changes.