Merge bitcoin/bitcoin#32631: refactor: Convert GenTxid to std::variant

a60f863d3e scripted-diff: Replace GenTxidVariant with GenTxid (marcofleon)
c8ba199598 Remove old GenTxid class (marcofleon)
072a198ea4 Convert remaining instances of GenTxid to GenTxidVariant (marcofleon)
1b528391c7 Convert `txrequest` to GenTxidVariant (marcofleon)
bde4579b07 Convert `txdownloadman_impl` to GenTxidVariant (marcofleon)
c876a892ec Replace GenTxid with Txid/Wtxid overloads in `txmempool` (marcofleon)
de858ce2be move-only: make GetInfo a private CTxMemPool member (stickies-v)
eee473d9f3 Convert `CompareInvMempoolOrder` to GenTxidVariant (marcofleon)
243553d590 refactor: replace get_iter_from_wtxid with GetIter(const Wtxid&) (stickies-v)
fcf92fd640 refactor: make CTxMemPool::GetIter strongly typed (marcofleon)
11d28f21bb Implement GenTxid as a variant (marcofleon)

Pull request description:

  Part of the [type safety refactor](https://github.com/bitcoin/bitcoin/pull/32189).

  This PR changes the GenTxid class to a variant, which holds both Txids and Wtxids. This provides compile-time type safety and eliminates the manual type check (bool m_is_wtxid). Variables that can be either a Txid or a Wtxid are now using the new GenTxid variant, instead of uint256.

ACKs for top commit:
  w0xlt:
    ACK a60f863d3e
  dergoegge:
    Code review ACK a60f863d3e
  maflcko:
    review ACK a60f863d3e 🎽
  theStack:
    Code-review ACK a60f863d3e

Tree-SHA512: da9b73b7bdffee2eb9281a409205519ac330d3336094d17681896703fbca8099608782c9c85801e388e4d90af5af8abf1f34931f57bbbe6e9674d802d6066047

src/node/interfaces.cpp

@@ -667,11 +667,11 @@ public:
         LOCK(m_node.mempool->cs);
         return IsRBFOptIn(tx, *m_node.mempool);
     }
-    bool isInMempool(const uint256& txid) override
+    bool isInMempool(const Txid& txid) override
     {
         if (!m_node.mempool) return false;
         LOCK(m_node.mempool->cs);
-        return m_node.mempool->exists(GenTxid::Txid(txid));
+        return m_node.mempool->exists(txid);
     }
     bool hasDescendantsInMempool(const uint256& txid) override
     {