feat: add first-class assert action

[Agusx1211]

Summary

Adds a first-class assert primitive action. Today, asserting an on-chain invariant requires a hacky "assertion template" — an empty-body template whose skip_condition is the invariant, relying on the engine's post-execution check to throw. It's indirect, verbose, and the error can't say which invariant failed.

The assert action evaluates a comparison and throws a clear error if it doesn't hold (no broadcast, ever).

API

type: assert with arguments:

• ACTUAL comes from either to (+ signature, optional values) → eth_call, or actual → any value resolver
• Exactly one comparator key: eq, neq, gt, lt, gte, lte → the EXPECTED value
• Optional message included in the error output

Comparison composes the existing call and basic-arithmetic resolvers. On failure it throws assert failed[: message]: <describe> (actual=…, expected=…, op=…).

- type: assert
  name: check-deposit-manager
  arguments:
    to: "{{some-proxy}}"
    signature: "depositManager() returns (address)"
    eq: "{{expected-deposit-manager}}"

Changes

• src/lib/types/actions.ts — AssertAction type, registered as a primitive
• src/lib/core/engine.ts — execution logic; enforces exactly one comparator (rejects zero or multiple)
• src/lib/core/__tests__/assert-action.spec.ts — 25 tests
• README.md — docs section
• dist/ — rebuilt canonical artifacts

Testing

• Assert suite: 25/25 pass
• Full suite: 605/605 pass

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