[uint] conversion between uint types

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• I have searched the existing issues. There is no such request yet, but here's a request with the most similar vibe: #691

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• This is not a support question.

Question:
What is recommended way to convert one type of uint to another?

Background:
I've developed a high-level lib for creating custom DeFi-oriented types that are implemented in pure Rust, where uint types serve as underlying types.

Details:
In certain scenarios, I need to expand the type to prevent overflow in intermediate calculations. For instance, there are cases where I must extend the type from U256 to U512. I'm exploring the best approach to convert between different uint types.

Based on my observations, it seems that try_from is only implemented for primitive types. One option is to manually rewrite the u64 values, but I believe there might be a more elegant solution. Perhaps it's worth considering the addition of a try_from implementation for converting between types at the uint library level.

As an illustration, consider the following two types:

construct_uint! {
    pub struct U256(4);
}

construct_uint! {
    pub struct U512(8);
}

In this context, creating a U512 type based on a U256 instance could look like this:

U512::try_from(U256::MAX)

Are you willing to help with this request?
I am willing to create a proposal for implementation if the feature is deemed useful.

Start by reviewing the construct_uint! entry point and the existing conversion behavior for primitive types. Compare the U256 and U512 examples, then determine the intended success and overflow behavior for conversions between uint types; the work is done when that behavior is implemented and covered by tests.