Parse "the Nth of the month" as a day of the current month

[AdrianAtZyte]

Part of #1265.

[codspeed]

Merging this PR will not alter performance

✅ 7 untouched benchmarks

---

_{Comparing AdrianAtZyte:first-of-the-month-standalone (bb4c05a) with master (9073f25)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.94%. Comparing base (9073f25) to head (bb4c05a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1418   +/-   ##
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  Coverage   98.94%   98.94%           
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  Files         239      239           
  Lines        3521     3521           
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  Hits         3484     3484           
  Misses         37       37           

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[serhii73]

Thanks! the 15th of the month now gives the 15th instead of 15 months ago. The simplification
of the month → of this month applies to any English text, though, so in search_dates every
"X of the month" phrase becomes a relative date for today, and it can cost a real date:

from datetime import datetime
from dateparser.search import search_dates

S = {"RELATIVE_BASE": datetime(2026, 9, 30, 13, 15)}
print(search_dates("Photo of the month, 12 March 1999", settings=S))
print(search_dates("He was named player of the month for March 2021.", settings=S))
print(search_dates("Employee of the month", settings=S, languages=["en"]))

input	master	this branch
Photo of the month, 12 March 1999	12 March 1999 → 1999-03-12	March → 2026-03-30, 1999 → 1999-09-30
He was named player of the month for March 2021.	March 2021	of the month → 2026-09-30 13:15, March 2021
Employee of the month (en)	None	of the month → 2026-09-30 13:15

The same goes for "Deal of the month", "Book of the month club", "the rest of the month" and so on, and
parse("of the month") returns today.

Anchoring the simplification to the day number seems enough, e.g. (\d+(?:st|nd|rd|th)?) of the month
→ \1 of this month. With that, the new tests still pass, the "Nth of the month" results are the
same, and the examples above give the same results as master.