Lightweight Choregraphic-programming based Multi-agent harness for effectful

[kiranandcode]

This PR implements the idea discussed with @eb8680 of using choreographic programming to implement a concise mechanism for specifying complex persistent programs.

def build_project(
    project_spec: str,
    architect: ArchitectAgent,
    coder: CoderAgent,
    reviewer: ReviewerAgent,
) -> list[ReviewResult]:
    """Choreographic program describing the full build workflow.

    1. Architect breaks the project into module specs.
    2. Coders implement modules in parallel (scatter distributes via claim-based pull).
    3. Reviewers review modules in parallel; coders fix in parallel until all pass.
    """
    # Step 1: Architect plans modules
    plan = architect.plan_modules(project_spec)
    modules = plan["modules"]

    # Step 2: Scatter implementation across coders
    scatter(modules,coder,lambda c, mod: c.implement_module(mod))

    # Step 3: Review loop
    while True:
        reviews = scatter(modules, reviewer,
            lambda r, mod: r.review_module(mod["module_path"], mod["test_path"]),
        )

        needs_fixes = [(mod, review)
            for mod, review in zip(modules, reviews)
            if review["verdict"] == "NEEDS_FIXES"
        ]

        if not needs_fixes:
            return reviews

        scatter(needs_fixes, coder,
            lambda c, (mod, review): c.implement_module(
                mod, fix_feedback=review["feedback"]
            )
        )

Describes a complex non-trivial multi-agent interaction of several agents with persistence, pull-based load balancing and agents with separate tasks, and a persistent task queue for resuming after crashes.

Addresses #603, Builds on top of #604, this also comes nicely full circle and provides a third stab at concurrency in effectful.

As always, concurrency is a boundless source of bugs and errors, so having a few extra eyes on this would be appreciated! I assume we'll have to iterate a bit on the design as well, but I'm very hopeful as to the direction this is going, because it seems to simplify a lot of annoying/hard-to-get-right boilerplate into a simple and concise mechanism!

[kiranandcode]

Iterating on this design using https://github.com/kiranandcode/VerifiedJS/blob/main/agents/verified_compiler_agents.py as a testbed: