NU7 testnet v0.1.2

NU7 testnet pre-release v0.1.2.

Changes since v0.1.1:

• feat(sync): batch block downloads to speed up sync from few peers — new [sync] block_download_batch_size option (default 100). Blocks now stream back-to-back from a single peer per request, so syncing from only a few peers is no longer capped at one block per network round-trip. Set to 1 for the previous behavior.
• fix(docker): add missing workspace members to release build context.

Linux x86_64 zebrad binary and container artifacts are built and attached automatically by the Fork release artifacts workflow.