feat(gds-games): continuous-time differential game support

[rororowyourboat]

Problem

gds-games (ogs) models normal-form and extensive-form games with discrete strategy spaces. Continuous-time, continuous-action differential games (e.g. pursuit-evasion) are a fundamentally different formalism that the current DSL cannot express.

Proposed Solution

Extend gds-games or create a new module for differential games:

• Continuous state dynamics with multiple players
• Continuous action/control spaces per player
• Zero-sum and general-sum formulations
• Value function and saddle-point equilibria
• Integration with continuous-time gds-sim (see feat(gds-sim): continuous-time ODE integration support #122)

Motivation

The Homicidal Chauffeur problem is a classical two-player zero-sum differential game. This class of problems (pursuit-evasion, Lanchester models, resource competition) is important for complex systems modeling but requires continuous dynamics.

Relationship to Existing Work

• gds-games handles discrete strategic interactions — this would be a separate formalism
• Would still compile to GDS canonical form (states, controls, dynamics)
• Depends on feat(gds-sim): continuous-time ODE integration support #122 (continuous-time ODE support)