scripted-diff: Rename NodeClockContext to FakeNodeClock

The previous name did not indicate the type was intended for
testing. Renaming to FakeNodeClock makes this explicit and
allows call sites to drop the ctx suffix on the variable name.

Suggested in #34858 review feedback.

-BEGIN VERIFY SCRIPT-
s() { git grep -l "$1" -- src | xargs sed -i "s/$1/$2/g"; }

s '\<NodeClockContext\>' 'FakeNodeClock'
s '\<clock_ctx\>'        'clock'
-END VERIFY SCRIPT-

src/test/fuzz/process_message.cpp

@@ -83,7 +83,7 @@ FUZZ_TARGET(process_message, .init = initialize_process_message)
     connman.Reset();
     auto& chainman{static_cast<TestChainstateManager&>(*node.chainman)};
     const auto block_index_size{WITH_LOCK(chainman.GetMutex(), return chainman.BlockIndex().size())};
-    NodeClockContext clock_ctx{1610000000s}; // any time to successfully reset ibd
+    FakeNodeClock clock{1610000000s}; // any time to successfully reset ibd
     chainman.ResetIbd();
     chainman.DisableNextWrite();
 
@@ -116,7 +116,7 @@ FUZZ_TARGET(process_message, .init = initialize_process_message)
     connman.AddTestNode(p2p_node);
     FillNode(fuzzed_data_provider, connman, p2p_node);
 
-    clock_ctx.set(ConsumeTime(fuzzed_data_provider));
+    clock.set(ConsumeTime(fuzzed_data_provider));
 
     CSerializedNetMsg net_msg;
     net_msg.m_type = random_message_type;