test(device-profiler): add edge case tests for JSON output

[groupsky]

Description

Several edge cases in the JSON output implementation are not currently tested.

Missing Test Scenarios

1. Port Parameter Fallback

Test when port is undefined (should default to empty string):

it('should handle undefined port in JSON output', async () => {
  await runProfileScan({
    transport: mockTransport,
    type: RegisterType.Holding,
    startAddress: 0,
    endAddress: 0,
    format: 'json',
    // port not provided
  })
  
  const output = JSON.parse(mockConsoleLog.mock.calls[0][0])
  expect(output.connection.port).toBe('')
})

2. Large Scan Performance

Test with 1000+ registers to verify memory behavior:

it('should handle large scans (1000+ registers)', async () => {
  // Mock 1000 register reads
  // Verify JSON output is valid and complete
})

3. Invalid/Malformed Data

Test robustness against edge cases:

it('should handle registers with all zeros', async () => {
  // value: Buffer.from([0x00, 0x00]) → "0000"
})

it('should handle registers with all ones', async () => {
  // value: Buffer.from([0xff, 0xff]) → "ffff"
})

it('should handle very large timing values', async () => {
  // timing: 999999 (nearly 17 minutes)
})

4. Empty Error Messages

Test behavior with falsy error values:

it('should handle empty error message strings', async () => {
  const result = {
    error: '',  // Empty string (falsy)
    errorType: 'unknown'
  }
  // Should error field be included or omitted?
})

Priority

• Port fallback: Medium (common scenario)
• Large scans: Low (edge case, but good to verify)
• Malformed data: Low (defensive programming)
• Empty errors: Low (unlikely in practice)

Files to Update

• packages/device-profiler/src/cli.test.ts
• packages/device-profiler/src/json-formatter.test.ts

Related

Identified in aspected review of #<PR_NUMBER>