Merge bitcoin/bitcoin#24213: refactor: use Span in random.*

3ae7791bca refactor: use Span in random.* (pasta)

Pull request description:

  ~This PR does two things~
  1. use a Span<unsigned char> for GetRandBytes and GetStrongRandBytes

  ~2. make GetRand a template for which any integral type can be used, where the default behavior is to return a random integral up to the max of the integral unless a max is provided.
  This simplifies a lot of code from `GetRand(std::numeric_limits<uint64_t>::max()` -> `GetRand<uint64_t>()`~

  MarcoFalke this was inspired by your comment here: https://github.com/bitcoin/bitcoin/pull/24185#issuecomment-1025514263 about using Span, so hopefully I'll be able to get this PR done and merged 😂

  ~Also, if requested I could revert the `GetRand(std::numeric_limits<uint64_t>::max()` -> `GetRand<uint64_t>()` related changes if it ends up causing too many conflicts~

ACKs for top commit:
  laanwj:
    Thank you! Code review re-ACK 3ae7791bca

Tree-SHA512: 12375a83b68b288916ba0de81cfcab4aac14389a66a36811ae850427435eb67dd55e47df9ac3ec47db4e214f4330139e548bec815fff8a3f571484ea558dca79

src/key.cpp

@@ -159,7 +159,7 @@ bool CKey::Check(const unsigned char *vch) {
 
 void CKey::MakeNewKey(bool fCompressedIn) {
     do {
-        GetStrongRandBytes(keydata.data(), keydata.size());
+        GetStrongRandBytes(keydata);
     } while (!Check(keydata.data()));
     fValid = true;
     fCompressed = fCompressedIn;
@@ -244,7 +244,7 @@ bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
     }
     unsigned char rnd[8];
     std::string str = "Bitcoin key verification\n";
-    GetRandBytes(rnd, sizeof(rnd));
+    GetRandBytes(rnd);
     uint256 hash;
     CHash256().Write(MakeUCharSpan(str)).Write(rnd).Finalize(hash);
     std::vector<unsigned char> vchSig;
@@ -397,7 +397,7 @@ void ECC_Start() {
     {
         // Pass in a random blinding seed to the secp256k1 context.
         std::vector<unsigned char, secure_allocator<unsigned char>> vseed(32);
-        GetRandBytes(vseed.data(), 32);
+        GetRandBytes(vseed);
         bool ret = secp256k1_context_randomize(ctx, vseed.data());
         assert(ret);
     }