Improve public re-exports

[tcharding]

Improve the public exports in two ways:

1. Inline re-exports into the docs of the module that re-exports them.
2. Separate public and private use statements

Recently we discussed a way to separate the public and private import statements to make the code more clear and prevent rustfmt joining them all together.

Separate public exports using a code block and #[rustfmt::skip]. Has the nice advantage of reducing the number of #[doc(inline)] attributes also.

1. Modules first, as they are part of the project's structure.
2. Private imports
3. Public re-exports (using rustfmt::skip to prevent merge)

Use the format

mod xyz;
mod abc;

use ...;

pub use {
    ...,
};

This patch introduces changes to the rendered HTML docs.

[tcharding]

Based on discussion here: https://github.com/rust-bitcoin/rust-bitcoin/discussions/2088