Created bianry_to_excessthree.py

[Craniace]

Describe your change:

Added a new algorithm for Binary to Excess-3 Code Conversion in the digital_logic directory.
The algorithm converts a binary input (as a string) into its 4-bit Excess-3 representation.
This is useful in digital electronics for encoding decimal digits into self-complementary binary codes.

• [x] Add an algorithm

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, separate PRs will be opened for other algorithms if needed.
• [x] All new Python files are placed inside an existing directory (e.g., digital_logic/).
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All function and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] The new algorithm includes at least one URL that points to Wikipedia or another similar explanation.

Reference:
Excess-3 Code - Wikipedia