v1.3.0 — single-word bit staging

What you get

• The bit writer is up to 1.2x faster on bit-packed writes and 1.36x on byte runs. Wide values stage through a single 32-bit word instead of a split 64-bit pair — fewer BigInt boundary crossings on the hot path. Wire bytes are identical, held by the golden battery and a 65,536-byte old-vs-new identity sweep.
• The flush contract is now tested at its edges: a write ending exactly on a 32-bit boundary zeroes its full 8-byte span, and the new tail suite pins every ending in [0, 384] bits against buffer reuse.

Wire compatible with the whole serialize family, as always.