Compare asymmetric keys by value through the base interface

[Xor-el]

Summary

TAsymmetricKeyParameter.Equals (the base IAsymmetricKeyParameter.Equals) compared only the
public/private flag: Result := FPrivateKey = AOther.PrivateKey. So any two public keys — or any two
private keys — held as the base IAsymmetricKeyParameter compared equal regardless of their key
material. Callers that only have the base interface (chain/credential code comparing a leaf's key
against a candidate) had no correct value comparison available; the real value equality lived on the
family sub-interfaces (IRsaKeyParameters.Equals, IECPublicKeyParameters.Equals, …) as typed
overloads, unreachable without first knowing the concrete family.

Change

The base Equals now routes through a protected virtual SameKey hook that every concrete key type
overrides:

• Classical families (RSA, EC, Ed25519/Ed448, X25519/X448, DH, DSA, BIP-340) dispatch to their
  existing typed Equals after a family Supports check — so a key of another family is simply not
  equal.
• PQ families (ML-DSA, ML-KEM, SLH-DSA) compare the parameter set (SameText on the parameters'
  name — nil-safe, and distinguishes same-length sets such as SLH-DSA sets sharing n, or ML-DSA
  pure vs pre-hash) plus a constant-time compare of the encoded key.
• The base default is fail-closed identity, so an un-overridden key type is equal only to itself.

Equals returns False for nil and never raises: DH and DSA additionally tolerate nil domain
parameters (consistent with their existing GetHashCode nil-guard).

SameKey is a protected hook rather than an override of Equals because a virtual override of a
method that also has typed reintroduce; overload siblings does not compile cleanly across both
supported compilers; the hook keeps a single interface-visible Equals while letting each family
supply the comparison.

Tests

Added TestBaseInterfaceEqualsComparesValue (RSA, via the base IAsymmetricKeyParameter): equal key
material compares equal, differing material does not (a flag-only check would wrongly say equal), a
key equals itself, and a key does not equal nil.

Full suite green on FPC x86_64, FPC i386, and Delphi Win32 (1577 tests, 0 failures on each).