Bump version to v5.9.3 and add RPC command reference

Pairs net.h heartbeat-throttle field with the IBD header-sync fix
in 2a484e4, and ships a full RPC reference doc.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/clientversion.h

@@ -8,7 +8,7 @@
 // These need to be macros, as version.cpp's and triangles-qt.rc's voodoo requires it
 #define CLIENT_VERSION_MAJOR       5
 #define CLIENT_VERSION_MINOR       9
-#define CLIENT_VERSION_REVISION    2
+#define CLIENT_VERSION_REVISION    3
 #define CLIENT_VERSION_BUILD       0
 
 // Converts the parameter X to a string after macro replacement on X has been performed.

src/net.h

@@ -277,6 +277,7 @@ public:
     uint256 hashLastGetHeadersEnd;
     int nStartingHeight;
     int64_t nLastTipCheck;   // last time we asked this peer for chain tip
+    int64_t nLastIbdHeaderRequest; // last time we sent IBD-mode getheaders to this peer (heartbeat throttle)
     int64_t nAvgBlockLatencyUs;  // rolling average block delivery latency (microseconds)
     int nBlocksDelivered;        // count of blocks delivered by this peer
     int nBestKnownHeight;        // highest block height known to this peer (updated from inv/block msgs)
@@ -336,6 +337,7 @@ public:
         hashLastGetHeadersEnd = 0;
         nStartingHeight = -1;
         nLastTipCheck = 0;
+        nLastIbdHeaderRequest = 0;
         nAvgBlockLatencyUs = 0;
         nBlocksDelivered = 0;
         nBestKnownHeight = -1;