feat: duration seconds; required fields; type-validated insertions/updates/retrievals

- Duration literals now accept s/m/h/d/w (was m/h/d/w): 'BEHAVES { ttl 30s }'
  is 30s, and 'within 30s' temporal expressions parse.
- Definition fields are REQUIRED by default ('field: type'); 'field: type?'
  marks a field optional. addNode enforces presence on insert, getSchema
  exposes per-field requiredness, and updateNodeData still validates the
  provided fields' types.
- Provider-returned edges are validated against the fact's declared typing:
  a value-carrying fact must return { value, possibility } with a value of the
  declared type (bare-number shorthand is rejected); a non-value fact must not
  carry a value; and every possibility must lie in [0, 1]. Violations throw a
  clear provider-authoring error instead of silently injecting malformed edges.

Tests: DSLRuntimeTyping (duration units, required-field enforcement, schema
requiredness, value-type + shape + possibility validation).

tests/DSLRuntimeExt.test.js

@@ -14,8 +14,8 @@ import { Arbiter } from '@arbiter/core';
 import { DSLRuntime } from '../src/runtime/DSLRuntime.js';
 
 const BASE_DSL = `
-  definition Employee { id: string level: number active: boolean }
-  definition Doc { id: string created: timestamp }
+  definition Employee { id: string? level: number? active: boolean? }
+  definition Doc { id: string? created: timestamp? }
   fact *owns(user: Employee, doc: Doc)
   fact *banned(user: Employee)
   evidence can_read(user: Employee, doc: Doc) { owns(user, doc) }
@@ -73,8 +73,8 @@ describe('DSLRuntime extended', () => {
     // edge for a DIFFERENT injectable fact that can_open also requires via
     // composition — here we add a transitive requirement to prove the loop.
     const dsl = `
-      definition Employee { id: string }
-      definition Doc { id: string }
+      definition Employee { id: string? }
+      definition Doc { id: string? }
       fact *owns(user: Employee, doc: Doc)
       fact *granted(user: Employee, doc: Doc)
       evidence base_read(user: Employee, doc: Doc) { owns(user, doc) }