BUG: Fixed DataFrame.resample() generating errors when bin edges fall on DST transitions

[presidentjacob]

Problem Description
DataFrame.resample() on DataFrames where edges exist in DST gaps would cause NonExistentTimeError instead of handling DST gracefully and pushing time forward by 1 hour.

Root Cause
The resampling bin-edge construction assumed calendar-day anchors like local midnight always exist in the timezone of the target. Around DST transitions where midnight is a non-existent local time (such as Africa/Cairo on April 26th, where 00:00:00 does not exist), the assumption causes failures. Edge generation produced invalid boundaries.

Fix
Fix strips the timezone before normalizing to avoid hitting the nonexistent local time. The returned tz-naive timestamps are re-localized by the date_range call in _get_time_bins via nonexistent="shift_forward"

In _get_timestamp_range_edges in pandas/core/resample.py:

if first.tz is not None:
      first = first.tz_localize(None)
      first = first.normalize()
else:
      first = first.normalize()

if last.tz is not None:
      last = last.tz_localize(None)
      last = last.normalize()
else:
      last = last.normalize()

if closed == "left":
      first = Timestamp(freq.rollback(first))
else:
      first = Timestamp(first - freq)

last = Timestamp(last + freq)

• closes BUG: DataFrame.resample() fails across DST transitions with NonExistentTimeError in timezone-aware data #62601
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
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[Liam3851]

If I understand correctly this appears to also be a suggested fix for issues #40517, #30378, and #62602. Note also related (but unmerged!) PRs #41043 and #62633. Issue #40517 had discussion coalescing around a universal shift_forward in normalize being the correct solution.