Introduce VectorLWECipherText with cached validation flag

[arcturusannamalai]

• Introduce VectorLWECipherText with cached validation flag
  • this has potential to speedup the evaluation of binary operators etc.
• early exit when possible

[yspolyakov]

I suggest discussing this further. The idea of adding a vector of LWE ciphertexts is reasonable but it is worth discussing how to do it first.

[arcturusannamalai]

@yspolyakov - thank you for the note; there are few use cases:

• the same argument sets are used to compute functions f and g and this type of caching can help
• lowering primitives from various transpilers maybe ensuring uniqueness of the cipher-text arguments to the OPenFHE primitives we can indicate uniqueness already

As for the implementation I can think of two strategies,

• Global register of vectors which are unique or not and update it (not my choice of implementation since its hard to do it threadsafe)
• Current implementation (need polish perhaps to propagate the solution through the OPenFHE API instead of wrap the arguments locally like I have done) where each vector stores its validation flag within it; perhaps the validate() method could be private and set only at c-tor time or by invoking at the time of OPenFHE binary operator etc.

Let me know what are your thoughts