Add PoDC-based router and supporting classes

[ilushaKolosov]

Introduce a PoDC routing protocol for evaluation in The ONE

Intent:
This change explores a routing strategy where forwarding behavior is influenced by delivery-related work credits, so nodes that contribute to successful deliveries are less likely to be filtered out in future forwarding decisions.

Design overview:

• Each forwarded data message carries an append-only proof chain.
• When the destination receives the message, it creates an ACK payload derived from the observed path.
• On ACK processing, participating nodes receive decayed work contributions based on their position in the confirmation path.
• Node score is computed from work and connectivity, and used as a lightweight forwarding filter for data messages.
• ACK messages are not score-filtered to avoid blocking credit propagation.

Scope of this commit:

• Adds PoDCRouter and related PoDC support classes (proof entries, ACK payload, metrics, crypto helpers).
• Adds minimal Message support for transporting proof-chain metadata.
• Keeps the contribution focused on Java simulator logic; local experiment artifacts and helper scripts are excluded from version control.

Note:
This is a research-oriented prototype intended for review and discussion, not a claim of production-ready protocol hardening.