Support various NTT

[juny2400]

Support various NTT types (negacyclic & cyclic)

Summary

Refactors the single negacyclic NTT into a pluggable class hierarchy that supports multiple transform types, adds a hem(HEAAN)-compatible
cyclic NTT, and introduces a real-encryption path built on it.

Changes

• NTT class hierarchy (NTT.hpp/.cpp): introduces abstract NTT_base with two concrete implementations — NTT (negacyclic, prime ≡ 1
  mod 2N) and NTT_C (cyclic / hem-compatible, prime ≡ 1 mod 4N, lands on the same NTT-domain bins as hem). Adds a runtime makeNTT()
  factory.
• New NTTConfig module (NTTConfig.hpp/.cpp): NTTType (NONNTT / NEGACYCLIC / CYCLIC) and NTTRootType (MIN / DIRECT / CUSTOM) enums, a
  global root-type setting with a ScopedNTTRootType RAII guard, and registerCustomPsi() for user-supplied primitive roots.
• Pluggable custom NTT: setNTTFactory() / createNTT() let callers register a custom backend (e.g. SIMD/HW-accelerated) that's picked up
  everywhere internally, with fallback to the default for combinations the factory doesn't handle.
• NTT metadata propagation: CKKSTypes, Encryptor, SecretKeyGenerator, etc. now record and forward the NTT type & root type.
• Real-encryption path: adds EncryptOptions::RealEncrypt() (cyclic-NTT based real-valued encryption), a new
  examples/EnDecryption-Real.cpp, and expanded EnDecryption-test.cpp / NTT-test.cpp coverage.