Changes to make clocks load in IO dispatcher

This CL aims at making sure that clock loading operations happen in a
seperate IO dispatcher which does not cause the main thread to block
while the clocks are being loaded. We use limited parallelism value as 1
since it allows execution of all clock operations (loading, sending of
events, etc.) in a sequential manner.

Bug: b/312519936
Test: Tested by building and flashing on local, also by adding log
statements and seeing whether all operations are running on same thread
or not, also by perfetto trace.
Flag: N/A

Change-Id: Ibd6ac2fc5bec4d4d6636492dfb04a28344be0914