feat: Repeating operations for util::async (#1776)

Async framework needed a way to do repeating operations (think simplest
cases like AmendmentBlockHandler).
This PR implements the **absolute minimum**, barebones repeating
operations that
- Can't return any values (void)
- Do not take any arguments in the user-provided function
- Can't be scheduled (i.e. a delay before starting repeating)
- Can't be stopped from inside the user block of code (i.e. does not
have stop token or anything like that)
- Can be stopped through the RepeatedOperation's `abort()` function (but
not from the user-provided repeating function)

src/rpc/RPCHelpers.cpp

@@ -45,7 +45,6 @@
 #include <fmt/core.h>
 #include <xrpl/basics/Slice.h>
 #include <xrpl/basics/StringUtilities.h>
-#include <xrpl/protocol/XRPAmount.h>
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/basics/chrono.h>
 #include <xrpl/basics/strHex.h>
@@ -75,6 +74,7 @@
 #include <xrpl/protocol/TxFormats.h>
 #include <xrpl/protocol/TxMeta.h>
 #include <xrpl/protocol/UintTypes.h>
+#include <xrpl/protocol/XRPAmount.h>
 #include <xrpl/protocol/jss.h>
 #include <xrpl/protocol/nftPageMask.h>
 #include <xrpl/protocol/tokens.h>

src/rpc/RPCHelpers.hpp

@@ -40,7 +40,6 @@
 #include <boost/regex/v5/regex_fwd.hpp>
 #include <boost/regex/v5/regex_match.hpp>
 #include <fmt/core.h>
-#include <xrpl/protocol/XRPAmount.h>
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/json/json_value.h>
 #include <xrpl/protocol/AccountID.h>
@@ -61,6 +60,7 @@
 #include <xrpl/protocol/Seed.h>
 #include <xrpl/protocol/TxMeta.h>
 #include <xrpl/protocol/UintTypes.h>
+#include <xrpl/protocol/XRPAmount.h>
 
 #include <chrono>
 #include <cstddef>