Memoize isPortable() and add error logging

[Copilot]

Applies review feedback from PR #344 to improve CPU feature detection error handling and efficiency.

Changes:

• Memoize isPortable() result - Cache the detection result in a module-level variable to prevent redundant require('cpu-features') attempts and duplicate warning logs when called multiple times during binary download/installation

• Add error object to warning log - Pass the caught error to logger.warn() for better debugging visibility when CPU feature detection fails

// Before
catch (error) {
  logger.warn('Failed to detect CPU features, using portable binary');
  return true;
}

// After  
let cachedIsPortable: boolean | undefined = undefined;

function isPortable(): boolean {
  if (cachedIsPortable !== undefined) {
    return cachedIsPortable;
  }
  
  try {
    // ... detection logic sets cachedIsPortable ...
  } catch (error) {
    logger.warn('Failed to detect CPU features, using portable binary', error);
    cachedIsPortable = true;
  }
  
  return cachedIsPortable;
}

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