Merge bitcoin/bitcoin#25487: [kernel 3b/n] Decouple {Dump,Load}Mempool from ArgsManager

cb3e9a1e3f Move {Load,Dump}Mempool to kernel namespace (Carl Dong)
aa30676541 Move DEFAULT_PERSIST_MEMPOOL out of libbitcoinkernel (Carl Dong)
06b88ffb8a LoadMempool: Pass in load_path, stop using gArgs (Carl Dong)
b857ac60d9 test/fuzz: Invoke LoadMempool via CChainState (Carl Dong)
b3267258b0 Move FopenFn to fsbridge namespace (Carl Dong)
ae1e8e3756 mempool: Use NodeClock+friends for LoadMempool (Carl Dong)
f9e8e5719f mempool: Improve comments for [GS]etLoadTried (Carl Dong)
813962da0b scripted-diff: Rename m_is_loaded -> m_load_tried (Carl Dong)
413f4bb52b DumpMempool: Pass in dump_path, stop using gArgs (Carl Dong)
bd4407817e DumpMempool: Use std::chrono instead of weird int64_t arthmetics (Carl Dong)
c84390b741 test/mempool_persist: Test manual savemempool when -persistmempool=0 (Carl Dong)

Pull request description:

  This is part of the `libbitcoinkernel` project: #24303, https://github.com/bitcoin/bitcoin/projects/18

  -----

  This PR moves `{Dump,Load}Mempool` into its own `kernel/mempool_persist` module and introduces `ArgsManager` `node::` helpers in `node/mempool_persist_args`to remove the scattered calls to `GetBoolArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)`.

  More context can be gleaned from the commit messages.

  -----

  One thing I was reflecting on as I wrote this was that in the long run, I think we should probably invert the validation <-> mempool relationship. Instead of mempool not depending on validation, it might make more sense to have validation not depend on mempool. Not super urgent since `libbitcoinkernel` will include both validation and mempool, but perhaps something for the future.

ACKs for top commit:
  glozow:
    re ACK cb3e9a1e3f via `git range-diff 7ae032e...cb3e9a1`
  MarcoFalke:
    ACK cb3e9a1e3f 🔒
  ryanofsky:
    Code review ACK cb3e9a1e3f

Tree-SHA512: 979d7237c3abb5a1dd9b5ad3dbf3b954f906a6d8320ed7b923557f41a4472deccae3e8a6bca0018c8e7a3c4a93afecc502acd1e26756f2054f157f1c0edd939d

test/functional/mempool_persist.py

@@ -141,6 +141,16 @@ class MempoolPersistTest(BitcoinTestFramework):
             self.nodes[2].syncwithvalidationinterfacequeue()  # Flush mempool to wallet
             assert_equal(node2_balance, wallet_watch.getbalance())
 
+        mempooldat0 = os.path.join(self.nodes[0].datadir, self.chain, 'mempool.dat')
+        mempooldat1 = os.path.join(self.nodes[1].datadir, self.chain, 'mempool.dat')
+
+        self.log.debug("Force -persistmempool=0 node1 to savemempool to disk via RPC")
+        assert not os.path.exists(mempooldat1)
+        result1 = self.nodes[1].savemempool()
+        assert os.path.isfile(mempooldat1)
+        assert_equal(result1['filename'], mempooldat1)
+        os.remove(mempooldat1)
+
         self.log.debug("Stop-start node0 with -persistmempool=0. Verify that it doesn't load its mempool.dat file.")
         self.stop_nodes()
         self.start_node(0, extra_args=["-persistmempool=0"])
@@ -153,8 +163,6 @@ class MempoolPersistTest(BitcoinTestFramework):
         assert self.nodes[0].getmempoolinfo()["loaded"]
         assert_equal(len(self.nodes[0].getrawmempool()), 7)
 
-        mempooldat0 = os.path.join(self.nodes[0].datadir, self.chain, 'mempool.dat')
-        mempooldat1 = os.path.join(self.nodes[1].datadir, self.chain, 'mempool.dat')
         self.log.debug("Remove the mempool.dat file. Verify that savemempool to disk via RPC re-creates it")
         os.remove(mempooldat0)
         result0 = self.nodes[0].savemempool()