docs(pong): bound Pong.servers and Pong.properties to max 256 entries

[VasilevNStas]

Description

Documents a maximum entry count of 256 for both Pong.servers and Pong.properties. No wire changes.

Problem

Both Pong.servers (repeated Peer) and Pong.properties (repeated Property) had no documented upper bound. A compromised Node could return millions of entries, forcing the client to allocate unbounded memory before any application-level check can run — the outbound counterpart of issue #23 (Ping.canaries).

Changes

• Pong.properties: added "Max 256 entries; clients MUST reject a Pong carrying more."
• Pong.servers: added "Max 256 entries; clients MUST reject a Pong carrying more."

Migration

Clients should add a check after deserialising the Pong: if len(servers) > 256 or len(properties) > 256, discard the Pong and treat the Node as compromised.

Closes #25

[VasilevNStas]

@yegor256 @davvd plz review

[0crat]

@VasilevNStas Thanks for the contribution! You've earned +8 points for this: +16 as a basis; -8 for too few (2) hits-of-code. Please, keep them coming. Your running score is +68; don't forget to check your Zerocracy account too).