SPEC: the info gap after plugrl-server #108 (one connection closes, not the server) - #7

Updates the gap in 5.4 about a non-empty info that cannot be split per environment, to match plugrl-server #108. Merge after #108.

• Before #108, a mismatch reached an assert in the connection handler. That was fatal to the whole server: the connection closed with 1011, and the server stopped for every client. The gap said only that the connection closed. plugrl-server's docs audit reproduced the rest.
• Since #108, the server checks that the observations, rewards, both flags and a non-empty info each hold m entries. A mismatch is a protocol error: it closes that one connection with 1001 and plugrl-server-resync, and the other clients go on.
• The splitting rule is described more precisely. The server finds m at the top level of info or one level into a nested map, so {"episode": {...}} on its own splits correctly.