QUALITY: Test infrastructure warnings suggest axis label positioning defects

[krystophny]

PROBLEM: Test output reveals significant positioning discrepancies in axis label rendering between PNG and expected matplotlib behavior.

EVIDENCE:

• Test output shows axis label positioning issues:
  'X-axis label position: X: 324 (should be centered at 328), Gap from plot: 20 pixels'
  'Matplotlib expectation: xlabel should be ~40-50 pixels below plot'
  'Y-axis label position: Gap from plot: 51 pixels, Matplotlib expectation: ylabel should be ~50-60 pixels left of plot'

IMPACT:

• User plots may have incorrectly positioned labels
• Visual output doesn't match matplotlib standards
• Poor user experience with plot aesthetics

SOLUTION:

1. Review axis label positioning algorithms
2. Implement proper text anchor point calculations
3. Add comprehensive positioning tests
4. Ensure PNG and PDF backends have consistent behavior

SEVERITY: MINOR - Visual quality issue affecting user experience

[krystophny]

Duplicate of #808; consolidating tick/axis label positioning defects under #808.