Import libart (#253)

This PR simply imports libart ( https://github.com/armon/libart ) and
its tests and integrates the code with cachegrand (style fixes, a few
bug fixes reported in the issues/prs, usage of xalloc, etc.) in
preparation to use it to build a map of how the data are replicated
across the infrastructure.

.github/workflows/build_and_test.yml

@@ -71,7 +71,7 @@ jobs:
       - name: Tests - Unit Tests
         working-directory: ${{github.workspace}}/build
         shell: bash
-        run: sudo tests/unit_tests/cachegrand-tests --order lex
+        run: cd tests/unit_tests && sudo ./cachegrand-tests --order lex
 
       - name: Code Coverage - Generation
         uses: danielealbano/lcov-action@v3

src/data_structures/art_spsc/LICENSE

@@ -0,0 +1,24 @@
+Copyright (c) 2012, Armon Dadgar
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+    * Neither the name of the organization nor the
+      names of its contributors may be used to endorse or promote products
+      derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL ARMON DADGAR BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.