Workflow Attributes

[devhawk]

Adds the ability for workflows to carry an arbitrary, JSON-serializable Map<String, Object> of custom attributes, recorded in the workflow status at creation, updatable afterward, and searchable via listWorkflows.

API

Set at creation — withAttributes(Map<String, Object>) added to every entry point:

• WorkflowOptions (context block: try (new WorkflowOptions().withAttributes(...).setContext()) { ... })
• StartWorkflowOptions
• DBOSClient.EnqueueOptions
• DebouncerClient / Debouncer

Filter — ListWorkflowsInput.withAttributes(Map) matches workflows whose attributes contain all the given pairs (Postgres @> containment, served by a GIN index).

Update after creation:

• DBOS.updateWorkflowAttributes(workflowId, attributes) — recorded as a step (DBOS.updateWorkflowAttributes) so it's exactly-once under recovery when called from within a workflow.
• DBOSClient.updateWorkflowAttributes(workflowId, attributes) — direct, for out-of-process use.
• Passing null (or an empty map) clears all attributes.

Other changes

• Scheduler startup fast-poll: polls schedules every 1s for the first 60s after launch so schedules registered around startup are picked up promptly; a ReentrantLock prevents the fast-path and regular polls from overlapping (Java-specific; py-transact's loop is single-threaded).
• Conductor ListQueuedWorkflowsRequest fix: now declares and forwards the attributes filter (previously hardcoded null)

fixes #434