Remove redundant async call in collection threads

This commit removes the redundant std:async call in the detached thread
launched for parsing and publishing the VPD for an individual FRU. Since
we have a dedicated detached thread for each FRU, we can do VPD parse
and publish in a synchronous manner from the detached thread itself,
instead of launching a asynchronous task which adds unnecessary
performance cost. This commit also handles any exception thrown while
launching the detached thread for a FRU. In case launching detached
thread for a FRU fails, we add the EEPROM path of the FRU to a "failed
EEPROM" list. This list can be handled by Manager later on.

Test:
```
- Install bitbaked image on Everest system.

- Check vpd-manager service status:
root@p10bmc:~# systemctl show vpd-manager -p NRestarts
NRestarts=0

- Check BMC reaches ready state:
root@p10bmc:~# obmcutil state
CurrentBMCState     : xyz.openbmc_project.State.BMC.BMCState.Ready
CurrentPowerState   : xyz.openbmc_project.State.Chassis.PowerState.On
CurrentHostState    : xyz.openbmc_project.State.Host.HostState.Running
BootProgress        : xyz.openbmc_project.State.Boot.Progress.
ProgressStages.OSRunning
OperatingSystemState: xyz.openbmc_project.State.OperatingSystem.Status.
OSStatus.Inactive

-Check CollectionStatus property of vpd-manager D-Bus service:
root@p10bmc:~# busctl get-property com.ibm.VPD.Manager /com/ibm/VPD/
Manager com.ibm.VPD.Manager CollectionStatus
s "Completed"

- Check execution time change
Measure the time between vpd-manager event loop start and
CollectionStatus = Completed on a Everest system. Following figures were
measured across 3 reboots:
- On current code, (with the extra async call) it is 61 secs.
- With the changes in this PR, it is 60.33 secs.
```

Change-Id: I86dd9f9f6a4c67b8159e4c90d6ffdb005568cf6b
Signed-off-by: Souvik Roy <souvikroyofficial10@gmail.com>
diff --git a/vpd-manager/include/worker.hpp b/vpd-manager/include/worker.hpp
index ac1b3d8..a9725c3 100644
--- a/vpd-manager/include/worker.hpp
+++ b/vpd-manager/include/worker.hpp
@@ -148,6 +148,21 @@
         return m_activeCollectionThreadCount;
     }
 
+    /**
+     * @brief API to get list of EEPROMs for which thread creation failed.
+     *
+     * This API returns reference to list of EEPROM paths for which VPD
+     * collection thread creation has failed. Manager needs to process this list
+     * of EEPROMs and take appropriate action.
+     *
+     * @return reference to list of EEPROM paths for which VPD collection thread
+     * creation has failed
+     */
+    inline std::forward_list<std::string>& getFailedEepromPaths() noexcept
+    {
+        return m_failedEepromPaths;
+    }
+
   private:
     /**
      * @brief An API to parse and publish a FRU VPD over D-Bus.
@@ -546,5 +561,8 @@
 
     // Counting semaphore to limit the number of threads.
     std::counting_semaphore<constants::MAX_THREADS> m_semaphore;
+
+    // List of EEPROM paths for which VPD collection thread creation has failed.
+    std::forward_list<std::string> m_failedEepromPaths;
 };
 } // namespace vpd