book: build sdk example

[alv-around]

Last week, I corrected some outdated documentation on the sdk usage (#1120). However, the two underlying problems were not address, which are:

1. There are currently no checkguards done on the sdk interface.

2. The code snippets in the documentation are hard-coded, which can lead to inconsistencies between the documentation and the actual code (as happened in book: sdk usage correction #1120)

In this PR, I tackle both problem by:

a. created a bin crate (sdk.rs) in the examples folder. This way, the compiler will run it's check on the code, and if anything if the interface changes this will trigger a compiler error on the example. This has also the advantage that the code is never run, against running expensive e2e tests.

I also rename the guest-example directory from example to guest to avoid any confusion with the generic cargo directory examples.

b. I linked in book the code snippets to the compiled code in a, to ensure that the code snippets are automatically updated so no extra effort is incurred in updating the docs.

[jonathanpwang]

LGTM! The idea to use snippets is really nice and an overall improvement.

Now that you've added the bin, should we change the target_path etc to the guest package so that if we wanted to, cargo run --example sdk would actually run?

I'll approve once I generate the docs locally to double check.

[jonathanpwang]

LGTM

[jonathanpwang]

Please fix lint

[alv-around]

Please fix lint

Sorry, that went completely under my radar. Is now fixed :)

[alv-around]

Now that you've added the bin, should we change the target_path etc to the guest package so that if we wanted to, cargo run --example sdk would actually run?

I purposely wrote examples/sdk.rs to not run out the box, because the binary executes very expensive operations. This way, I wanted to discourage accidental triggers of this binary.

I could have shadowed the variable target_path after line 59:
https://github.com/alv-around/openvm/blob/6ef5dab4ed7bdfdb5d8e1a268dac2f05b72e57e2/crates/sdk/examples/sdk.rs#L59
With:
https://github.com/alv-around/openvm/blob/6ef5dab4ed7bdfdb5d8e1a268dac2f05b72e57e2/crates/sdk/examples/sdk.rs#L47-L51

This way it would run out of the box, however this would have made the imports in the book a bit more convoluted. And I am not sure whether that make things better.

I think like this we have get the best of both worlds:

1. we tell the compiler: "this is how we want the users to use our product, please run your checks". But at the same time we don't run any expensive computation.
2. we export in a simple manner and straight-forward manner the documentation.

But am happy to change anything you consider most appropriate :)

[jonathanpwang]

^This makes sense. I think we can make a separate example repo with a runnable version (and without the heavier computation part) to complement.