Feature - Support "use step" in Class Instance Methods

Problem

Currently, the workflow system only supports "use step" in:

• Static methods
• Standalone functions
• Object methods

However, class instance methods cannot be marked with "use step", which limits the ability to create well-structured, stateful workflow components using object-oriented patterns.

This results in the following error:

Instance methods cannot be marked with "use step". Only static methods, functions, and object methods are supported.

Use Case

In complex workflow orchestration scenarios, managing state across multiple workflow steps would benefit greatly from class-based patterns. Here's a real-world example:

Current Workaround (Verbose & Error-Prone)

// Need to pass stream to every function call
async function emitEventStep(stream: WritableStream, event: Event) {
  "use step";
  const writer = stream.getWriter();
  try {
    await writer.write(event);
  } finally {
    writer.releaseLock();
  }
}

// Called dozens of times throughout the workflow
await emitEventStep(workflowStream, event1);
await emitEventStep(workflowStream, event2);
await emitEventStep(workflowStream, event3);
// ... repeated 20+ times

Desired Approach

class WorkflowStreamManager {
  private writer: WritableStreamDefaultWriter | null = null;
  private stream: WritableStream;
  private closed = false;

  constructor(stream: WritableStream) {
    this.stream = stream;
  }

  async write(event: Event) {
    "use step";  // Not supported
    
    if (this.closed) {
      console.warn("Stream already closed");
      return;
    }

    if (!this.writer) {
      this.writer = this.stream.getWriter();
    }

    await this.writer.write(event);
  }

  async close() {
    "use step";  // Not supported
    
    if (this.closed) return;
    this.closed = true;
    
    if (this.writer) {
      await this.writer.close();
      this.writer = null;
    }
  }
}

// Usage is much cleaner
const streamManager = new WorkflowStreamManager(workflowStream);
await streamManager.write(event1);
await streamManager.write(event2);
await streamManager.write(event3);
await streamManager.close();

Resource Management

class WorkflowResourceManager {
  async acquire(resource: string) { "use step"; /* ... */ }
  async release(resource: string) { "use step"; /* ... */ }
  async cleanup() { "use step"; /* ... */ }
}