Merge bitcoin/bitcoin#28721: multiprocess compatibility updates

3b70f7b6156cb110c47a6e482791cf337bb6ad6d doc: fix broken doc/design/multiprocess.md links after #24352 (Ryan Ofsky)
6d43aad742c7ea28303cf2799528188938e7ce32 span: Make Span template deduction guides work in SFINAE context (Ryan Ofsky)
8062c3bdb9dd3062597ed8299e99151b612d32b7 util: Add ArgsManager SetConfigFilePath method (Ryan Ofsky)
441d00c60f0a67889d23f8556190ff99dde488bc interfaces: Rename CalculateBumpFees methods to be compatible with capn'proto (Ryan Ofsky)
156f49d682ef025fb942c997a6c5475e18eef9cf interfaces: Change getUnspentOutput return type to avoid multiprocess segfault (Ryan Ofsky)
4978754c0058bbdfbcd492f25fa49ef211e11d6e interfaces: Add schedulerMockForward method so mockscheduler RPC can work across processes (Ryan Ofsky)
924327eaf3ada45a603e80aa4a3ab38a0f8c8673 interfaces: Fix const virtual method that breaks multiprocess support (Ryan Ofsky)
82a379eca8251c736b4de6e7a2516582641ce397 streams: Add SpanReader ignore method (Russell Yanofsky)

Pull request description:

  This is a collection of small changes to interfaces and code which were needed as part of multiprocess PR #10102, but have been moved here to make that PR smaller.

  All of these changes are refactoring changes which do not affect behavior of current code

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/issues/28722).

ACKs for top commit:
  achow101:
    ACK 3b70f7b6156cb110c47a6e482791cf337bb6ad6d
  naumenkogs:
    ACK 3b70f7b6156cb110c47a6e482791cf337bb6ad6d
  maflcko:
    re-ACK 3b70f7b6156cb110c47a6e482791cf337bb6ad6d  🎆

Tree-SHA512: 2368772b887056ad8a9f84c299cfde76ba45943770e3b5353130580900afa9611302195b899ced7b6e303b11f053ff204cae7c28ff4e12c55562fcc81119ba4c

1 files changed, 6 insertions, 4 deletions

diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 4c83df7eca..5ec7e17b26 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -328,10 +328,12 @@ public:
     std::vector<std::string> listRpcCommands() override { return ::tableRPC.listCommands(); }
     void rpcSetTimerInterfaceIfUnset(RPCTimerInterface* iface) override { RPCSetTimerInterfaceIfUnset(iface); }
     void rpcUnsetTimerInterface(RPCTimerInterface* iface) override { RPCUnsetTimerInterface(iface); }
-    bool getUnspentOutput(const COutPoint& output, Coin& coin) override
+    std::optional<Coin> getUnspentOutput(const COutPoint& output) override
     {
         LOCK(::cs_main);
-        return chainman().ActiveChainstate().CoinsTip().GetCoin(output, coin);
+        Coin coin;
+        if (chainman().ActiveChainstate().CoinsTip().GetCoin(output, coin)) return coin;
+        return {};
     }
     TransactionError broadcastTransaction(CTransactionRef tx, CAmount max_tx_fee, std::string& err_string) override
     {
@@ -670,7 +672,7 @@ public:
         m_node.mempool->GetTransactionAncestry(txid, ancestors, descendants, ancestorsize, ancestorfees);
     }
 
-    std::map<COutPoint, CAmount> CalculateIndividualBumpFees(const std::vector<COutPoint>& outpoints, const CFeeRate& target_feerate) override
+    std::map<COutPoint, CAmount> calculateIndividualBumpFees(const std::vector<COutPoint>& outpoints, const CFeeRate& target_feerate) override
     {
         if (!m_node.mempool) {
             std::map<COutPoint, CAmount> bump_fees;
@@ -682,7 +684,7 @@ public:
         return MiniMiner(*m_node.mempool, outpoints).CalculateBumpFees(target_feerate);
     }
 
-    std::optional<CAmount> CalculateCombinedBumpFee(const std::vector<COutPoint>& outpoints, const CFeeRate& target_feerate) override
+    std::optional<CAmount> calculateCombinedBumpFee(const std::vector<COutPoint>& outpoints, const CFeeRate& target_feerate) override
     {
         if (!m_node.mempool) {
             return 0;