PERF: _return_parsed_timezone_results

[lukemanley]

• closes PERF:cythonize _return_parsed_timezone_results? #50107 (Replace xxxx with the GitHub issue number)
• 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/v2.0.0.rst file if fixing a bug or adding a new feature.

@MarcoGorelli - thanks for the ping. I think this gets most of the bottleneck you highlighted:

import pandas as pd

dates = pd.date_range('1900', '2000').tz_localize('+01:00').strftime('%Y-%d-%m %H:%M:%S%z').tolist()
dates.append('2020-01-01 00:00:00+02:00')

%timeit pd.to_datetime(dates, format='%Y-%d-%m %H:%M:%S%z')

# 529 ms ± 24.5 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)   <- main
# 174 ms ± 977 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)  <- PR

[MarcoGorelli]

Well done, thanks! Looks good to me pending green, and nice to see that this could be solved without having to Cythonize