Merge bitcoin/bitcoin#33724: refactor: Return uint64_t from GetSerializeSize

fa6c0bedd3 refactor: Return uint64_t from GetSerializeSize (MarcoFalke)
fad0c8680e refactor: Use uint64_t over size_t for serialized-size values (MarcoFalke)
fa4f388fc9 refactor: Use fixed size ints over (un)signed ints for serialized values (MarcoFalke)
fa01f38e53 move-only: Move CBlockFileInfo to kernel namespace (MarcoFalke)
fa2bbc9e4c refactor: [rpc] Remove cast when reporting serialized size (MarcoFalke)
fa364af89b test: Remove outdated comment (MarcoFalke)

Pull request description:

  Consensus code should arrive at the same conclusion, regardless of the architecture it runs on. Using architecture-specific types such as `size_t` can lead to issues, such as the low-severity [CVE-2025-46597](https://bitcoincore.org/en/2025/10/24/disclose-cve-2025-46597/).

  The CVE was already worked around, but it may be good to still fix the underlying issue.

  Fixes https://github.com/bitcoin/bitcoin/issues/33709 with a few refactors to use explicit fixed-sized integer types in serialization-size related code and concluding with a refactor to return `uint64_t` from `GetSerializeSize`. The refactors should not change any behavior, because the CVE was already worked around.

ACKs for top commit:
  Crypt-iQ:
    crACK fa6c0bedd3
  l0rinc:
    ACK fa6c0bedd3
  laanwj:
    Code review ACK fa6c0bedd3

Tree-SHA512: f45057bd86fb46011e4cb3edf0dc607057d72ed869fd6ad636562111ae80fea233b2fc45c34b02256331028359a9c3f4fa73e9b882b225bdc089d00becd0195e

src/test/fuzz/block_index.cpp

@@ -12,6 +12,8 @@
 #include <txdb.h>
 #include <validation.h>
 
+using kernel::CBlockFileInfo;
+
 namespace {
 
 const BasicTestingSetup* g_setup;

src/test/fuzz/deserialize.cpp

@@ -17,6 +17,7 @@
 #include <net.h>
 #include <netbase.h>
 #include <netgroup.h>
+#include <node/blockstorage.h>
 #include <node/utxo_snapshot.h>
 #include <primitives/block.h>
 #include <protocol.h>
@@ -34,6 +35,7 @@
 #include <optional>
 #include <stdexcept>
 
+using kernel::CBlockFileInfo;
 using node::SnapshotMetadata;
 
 namespace {

src/test/fuzz/miniscript.cpp

@@ -1120,7 +1120,7 @@ void TestNode(const MsCtx script_ctx, const NodeRef& node, FuzzedDataProvider& p
         assert(mal_success);
         assert(stack_nonmal == stack_mal);
         // Compute witness size (excluding script push, control block, and witness count encoding).
-        const size_t wit_size = GetSerializeSize(stack_nonmal) - GetSizeOfCompactSize(stack_nonmal.size());
+        const uint64_t wit_size{GetSerializeSize(stack_nonmal) - GetSizeOfCompactSize(stack_nonmal.size())};
         assert(wit_size <= *node->GetWitnessSize());
 
         // Test non-malleable satisfaction.