fix: Remove vendored boost file to compile with boost 1.87. (#471)

BEGIN_COMMIT_OVERRIDE
fix: Remove vendored boost file to compile with boost 1.87.
fix: Update usage of the steady_timer to be compatible with boost 1.87.
fix: Remove type alias import for JSON system_error that was removed in
boost 1.87.
END_COMMIT_OVERRIDE

Author: kinyoklion

libs/client-sdk/src/flag_manager/flag_store.cpp

@@ -1,5 +1,3 @@
-#include <boost/json/system_error.hpp>
-
 #include "flag_store.hpp"
 
 #include <launchdarkly/encoding/sha_256.hpp>

libs/internal/src/events/asio_event_processor.cpp

@@ -168,7 +168,7 @@ void AsioEventProcessor<SDK>::ScheduleFlush() {
     LD_LOG(logger_, LogLevel::kDebug) << "event-processor: scheduling flush in "
                                       << flush_interval_.count() << "ms";
 
-    timer_.expires_from_now(flush_interval_);
+    timer_.expires_after(flush_interval_);
     timer_.async_wait([this](boost::system::error_code ec) {
         if (ec) {
             LD_LOG(logger_, LogLevel::kDebug)

libs/internal/src/events/request_worker.cpp

@@ -109,7 +109,7 @@ void RequestWorker::OnDeliveryAttempt(network::HttpResult const& result,
                     << tag_ << "error posting " << batch_->Count()
                     << " event(s) (will retry): HTTP error " << result.Status();
             }
-            timer_.expires_from_now(retry_delay_);
+            timer_.expires_after(retry_delay_);
             timer_.async_wait([this, callback](boost::system::error_code ec) {
                 if (ec) {
                     return;

libs/server-sent-events/src/client.cpp

@@ -140,7 +140,7 @@ class FoxyClient : public Client,
 
         create_session();
         create_parser();
-        backoff_timer_.expires_from_now(backoff_.delay());
+        backoff_timer_.expires_after(backoff_.delay());
         backoff_timer_.async_wait(beast::bind_front_handler(
             &FoxyClient::on_backoff, shared_from_this()));
     }