Add testutils and test-wallet features

[notmandatory]

Description

This PR creates two new feature flags, testutils to enable the testutils module, and test-wallet to enable the now exposed wallet::get_funded_wallet() function. Exposing the wallet::get_funded_wallet() function and moving the Wallet::network() function are needed to make testing easier for supporting projects like bdk-reserves without including this functionality in non-test builds.

Notes to the reviewers

All doctests should work with the new testutils feature without having this module exposed for non-test builds.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• I've updated CHANGELOG.md

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[notmandatory]

@LLFourn I found another way here to add the testutils feature back in using bdk as it's own dev dependency. Too hacky? seem to work for doc tests and I don't see any down sides.

[LLFourn]

@notmandatory 🤯 . Did you get that idea from somewhere? can we not just add testutils as a default feature I guess then it will be available during doctests I guess?

[notmandatory]

It probably would work as a default feature but then anyone using BDK as a normal dependency would need to set no-default features or end with the unwanted 'testutils'. I ran across this in a old rustc bug where adding a crate as a test dep of itself used to panicked the compiler. But issue got fixed and seems to be supported.

[notmandatory]

This is the issue comment that gave me the idea:

rust-lang/cargo#2911 (comment)

[LLFourn]

They seem to say it doesn't work in that the hack enables it for non-dev as well: rust-lang/cargo#2911 (comment)

In rust you only pay for what you use so there is no real harm in not having it under a feature flag or as a default feature flag. My personal preference is to leave without and wait until rust-lang/rust#67295 and rust-lang/cargo#2911 are fixed.

[notmandatory]

Ok ya I read through a few more related issues and looks like this is a hack that will soon not be supported and as you said probably isn't doing what I think it is.

Closing this PR.