[SDK] Fix null handles (#474)

* Fix null handle

- use .handle=0, not .handle=numeric_limits<>::max()

* Update lib.common.hasher

* Fix ROCPROFILER_CONTEXT_NONE

* Use context operator==

* Update CHANGELOG

* Updated null handle for scratch memory and changed allocation test so that free ops account for null agent

---------

Co-authored-by: Ian Trowbridge <Ian.Trowbridge@amd.com>

source/lib/rocprofiler-sdk/hsa/memory_allocation.cpp

@@ -324,8 +324,7 @@ get_next_dispatch()
     return _v;
 }
 
-constexpr auto null_rocp_agent_id =
-    rocprofiler_agent_id_t{.handle = std::numeric_limits<uint64_t>::max()};
+constexpr auto null_rocp_agent_id = rocprofiler_agent_id_t{.handle = 0};
 
 struct memory_allocation_data
 {