Implement Probabilistic Logic Networks (PLN) inference rules:
- TruthValue struct with clamped strength/confidence
- deduction(): chain two implications A->B and B->C
- revision(): merge two independent truth estimates
- negation(): logical NOT (inverts strength, preserves confidence)
- conjunction(): logical AND (multiply strength, min confidence)
- score_with_evidence(): combine base score with confirmations and contradictions
10 unit tests covering basic operations, boundary cases,
symmetry, zero-confidence handling, and output bounds.
Part of #29
Implement Economic Attention Network (ECAN) for memory importance management:
- EcanParams: decay_rate, beta, spread_factor, threshold
- decay_sti(): STI decay toward zero over time
- update_lti(): LTI accumulation weighted by STI, penalized below threshold
- spread(): boost STI for confirmed memories
- cycle(): full decay + LTI update weighted by truth value
- initialize(): compute initial STI/LTI from truth value and confidence
14 unit tests covering decay convergence, LTI growth/penalty,
spread clamping, cycle behavior, initialization, and bounds.
Part of #29
