MAINT: Updated f-string method (#6230)

* MAINT: Used f-string method

Updated the code with f-string methods wherever required for a better and cleaner understanding of the code.

* Updated files with f-string method

* Update rsa_key_generator.py

* Update rsa_key_generator.py

* Update elgamal_key_generator.py

* Update lru_cache.py

I don't think this change is efficient but it might tackle the error as the error was due to using long character lines.

* Update lru_cache.py

* Update lru_cache.py

Co-authored-by: cyai <seriesscar@gmail.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

matrix/sherman_morrison.py

@@ -256,7 +256,7 @@ if __name__ == "__main__":
         v[0, 0], v[1, 0], v[2, 0] = 4, -2, 5
         print(f"u is {u}")
         print(f"v is {v}")
-        print("uv^T is %s" % (u * v.transpose()))
+        print(f"uv^T is {u * v.transpose()}")
         # Sherman Morrison
         print(f"(a + uv^T)^(-1) is {ainv.ShermanMorrison(u, v)}")