Performance improvements targeting slice allocation patterns and memory efficiency in queue operations.

Changes

• Slice insertion in AddJob: Replace double-append pattern with copy-based insertion

  // Before: O(n) extra allocation
  q.jobs = append(q.jobs[:idx], append([]Job{*job}, q.jobs[idx:]...)...)
  
  // After: In-place shift
  q.jobs = append(q.jobs, Job{})
  copy(q.jobs[idx+1:], q.jobs[idx:])
  q.jobs[idx] = *job

• Pre-allocate slices in Run() and Retry() with estimated capacity instead of growing dynamically

• Reuse slice capacity when clearing: execJobs = execJobs[:0] vs execJobs = []*Job{}

• Remove unnecessary allocation: Don't initialize Stacktrace to empty slice; nil is idiomatic

• Add benchmarks for key operations

Benchmark Results

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