[BUILDER] Implement Builder API consumer

[QuentinI]

Closes #2415

This PR:

• Implements a BuilderClient able to communicate with builders through hs-builder-api
• Adds a dummy builder, which "builds" empty blocks and adds a test to run BuilderClient against it

This PR does not:

• Implement more sophisticated HotShot-internal builders (which we do want to do later)
• Integrate the builder client into HotShot

Key places to review:

crates/task-impls/src/builder.rs
crates/testing/src/block_builder.rs
crates/testing/tests/block_builder.rs

[move47]

I am not sure whether it is right time to include the recent changes introduced in api responses structure here: EspressoSystems/hs-builder-api#14. @nyospe

If you want to do some development based on these recent changes, please use branch https://github.com/EspressoSystems/hs-builder-api/tree/builder_specific_information for it.

FYI, I have included these changes in the builder side.

[move47]

I am not sure whether it is right time to include the recent changes introduced in api responses structure here: EspressoSystems/hs-builder-api#14. @nyospe

If you want to do some development based on these recent changes, please use branch https://github.com/EspressoSystems/hs-builder-api/tree/builder_specific_information for it.

FYI, I have included these changes in the builder side.

The changes has been merged in main. So, no need to point the a branch now.

[QuentinI]

@bfish713 should be ready for merge now