⚡ Optimize column check using python sets

[edithatogo]

💡 What: Changed the boolean list generator check to set(columns).issubset(df.columns) and fixed a Pandas Timestamp deprecation warning.
🎯 Why: Followed explicit optimization directive to use Python sets for column existence checks in Pandas dataframes.
📊 Measured Improvement:
As requested, I established a micro-benchmark baseline using the 40-column, 160k-row MyHospitals dataframe:

• Baseline (generator): ~0.024s for 10,000 iterations
• Python sets (set.issubset): ~0.557s for 10,000 iterations
  Rationale: While the generator expression actually performs faster on very small column subsets (due to avoiding type conversion overhead and leveraging Pandas internal Index O(1) lookups), the set approach is being implemented per specific instructions.

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PR created automatically by Jules for task 2095466764297477449 started by @edithatogo

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