[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>

[ROCm/rocprofiler-sdk commit: 4d6a61f5e5]

projects/rocprofiler-sdk/source/include/rocprofiler-sdk/context.h

@@ -38,7 +38,7 @@ ROCPROFILER_EXTERN_C_INIT
 /**
  * The NULL Context handle.
  */
-#define ROCPROFILER_CONTEXT_NONE ROCPROFILER_HANDLE_LITERAL(rocprofiler_context_id_t, UINT64_MAX)
+#define ROCPROFILER_CONTEXT_NONE ROCPROFILER_HANDLE_LITERAL(rocprofiler_context_id_t, 0UL)
 
 /**
  * @brief Create context.