[core] Remove bdk_chain from dev-dependencies

[ValuedMammal]

The reason is to avoid a circular dependency, but it's a bit unclear whether this is actually an issue at the moment

[oleonardolima]

I think it'll be hard to do it, as we'll mostly already depend on bdk_testenv which already depends on bdk_chain (just wondering about it for now 🤔)

[evanlinjin]

@ValuedMammal how would this result in cyclic dependencies? One can't depend on a crate's tests?

[notmandatory]

I suggested this issue since it seems weird that bdk_core has even a test dependency on bdk_chain. It looks like the only reason for the dependency is that the bdk_core doc examples depend on bdk_chain. Is there any reason not to re-write the doc examples or move them to the chain crate?

[oleonardolima]

I suggested this issue since it seems weird that bdk_core has even a test dependency on bdk_chain. It looks like the only reason for the dependency is that the bdk_core doc examples depend on bdk_chain. Is there any reason not to re-write the doc examples or move them to the chain crate?

The test usage in block_id! is being moved to bdk_testenv at #1612, so it won't be an issue anymore. Also, it's weird it depends on bdk_chain::BlockId instead of crate::BlockId 🤔.

I think it's fine to either rewrite the doc examples or move to bdk_chain.