Add ascii_to_char conversion script (Fixes #13569)

[Vedavyasa21]

Describe your change:

• [Yes ] Add an algorithm?
• Fix a bug or typo in an existing algorithm?
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• Documentation change?

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Fixes #13569

Description
Added a new script ascii_to_char.py under the conversions module.
The function ascii_to_char(ascii_value: int) converts an ASCII integer to its corresponding character.
Example
ascii_to_char(65)
'A'

Details
Added input validation for range 0–127
Included doctest for quick verification
Code follows TheAlgorithms style and documentation format