COMPAT: make astype to datetime/timedelta types more robust

[jreback]

closes #19116

[codecov]

Codecov Report

Merging #19176 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #19176      +/-   ##
==========================================
+ Coverage   91.52%   91.54%   +0.02%     
==========================================
  Files         148      148              
  Lines       48778    48786       +8     
==========================================
+ Hits        44642    44662      +20     
+ Misses       4136     4124      -12

Flag	Coverage Δ
#multiple	89.91% <100%> (+0.02%)	⬆️
#single	41.61% <55.55%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/dtypes/cast.py	88.58% <100%> (+0.15%)	⬆️
pandas/plotting/_converter.py	66.95% <0%> (+1.73%)	⬆️

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