Add Rabin–Karp String Matching Algorithm (Fixes #13918)

This pull request adds the Rabin–Karp String Matching Algorithm to the strings/ directory.
Rabin–Karp is an important string-searching technique that uses rolling hash to efficiently detect pattern matches, especially useful for multiple-pattern search.

This implementation includes:

✔ Single Pattern Matching

Rolling hash–based substring search

Collision detection and verification

Efficient sliding-window hashing

✔ Multiple Pattern Matching

Groups patterns by length

Computes all pattern hashes once

Scans the text only a single time

Returns match indices for all patterns

✔ Optimized Version

Variant using a large prime modulus (1_000_000_007)

Significantly reduces hash collisions

✔ Documentation & Doctests

Full type hints

Comprehensive doctests

Examples covering edge cases: empty inputs, overlapping matches, collisions, no matches

Reference

Rabin–Karp Algorithm — https://en.wikipedia.org/wiki/Rabin%E2%80%93Karp_algorithm

Describe your change:

Add an algorithm?

Fix a bug or typo in an existing algorithm?

Add or change doctests?

Documentation change?

Checklist:

I have read CONTRIBUTING.md
.

This pull request is all my own work -- I have not plagiarized.

I know that pull requests will not be merged if they fail the automated tests.

This PR only changes one algorithm file.

All new Python files are placed inside an existing directory.

All filenames are in all lowercase characters with no spaces or dashes.

All functions and variable names follow Python naming conventions.

All function parameters and return values are annotated with Python type hints.

All functions have doctests that pass the automated testing.

All new algorithms include at least one URL that points to Wikipedia or similar explanation.

This pull request resolves the issue with a closing keyword: Fixes #13918.