server: include sessionId in the login success packet for 26.2+

[DallasCarraher]

Summary

26.2 (protocol 776) added a mandatory sessionId: UUID field to packet_success. The server-side login flow (src/server/login.js) built that packet without it, so the compiled protodef writer threw Write error for undefined : Cannot read properties of undefined (reading 'length') as soon as a 26.2 client logged in against a server built on this library. This doesn't affect clients connecting to a real Mojang server (which always supplies it) — only consumers who host their own server on this library (flying-squid, mineflayer's own test harness, etc).

Included unconditionally rather than gated behind a supportFeature check: protodef only reads the fields a version's schema actually defines, so this is inert on older versions' packet_success where the field doesn't exist — same pattern already used for properties: [] a few lines up.

Found and fixed while getting PrismarineJS/minecraft-data#1298 (26.2 data) working end-to-end against mineflayer.

Related:

• PrismarineJS/minecraft-data#1298 — 26.2 data
• PrismarineJS/prismarine-chunk#333 — 26.2 chunk implementation mapping
• PrismarineJS/prismarine-physics#143 — 26.2 liquid gravity feature
• mineflayer testedVersions bump (PR incoming)

Test plan

• Full suite against minecraft-data#1298's branch: 6787 passing, 73 pending, 2 failing — both pre-existing and unrelated (a 1.16.5 server-download timeout, and a 26.1 packet-fuzzer gap for the ItemStackTemplate type that predates this change). Zero failures attributable to 26.2.
• standard lint clean
• Manually confirmed: a local offline server + client pair on 26.2 now progresses cleanly through login and the full configuration phase (previously crashed immediately on the success packet write)