DOC: Warn about dtype inference with raw=True in DataFrame.apply

[pranavkp71]

• closes DOC: warn about apply with raw=True, if function returns Optional[int] #61632
• Adds a note in DataFrame.apply docstring explaining that when raw=True,
  the dtype is inferred from the first returned value, and returning None
  may cause a TypeError.
• All pre-commit checks passed.

[pranavkp71]

This PR adds a note to the DataFrame.apply docstring to warn users about dtype inference when using raw=True, addressing issue #61632.