Use valgrind to simplify no-leak regression testing

[vaind]

Seems like we can detect leaks using valgrind:

dart2native ./test/box_test.dart -o box-test
valgrind --show-mismatched-frees=no ./box-test

==13549== LEAK SUMMARY:
==13549==    definitely lost: 0 bytes in 0 blocks
==13549==    indirectly lost: 0 bytes in 0 blocks
==13549==      possibly lost: 0 bytes in 0 blocks
==13549==    still reachable: 91,012 bytes in 188 blocks
==13549==         suppressed: 0 bytes in 0 blocks

And If I manually comment out a free() call on an ffi.Pointer (e.g. in box.count()), it shows a leak:

==13580== LEAK SUMMARY:
==13580==    definitely lost: 128 bytes in 16 blocks
==13580==    indirectly lost: 0 bytes in 0 blocks
==13580==      possibly lost: 0 bytes in 0 blocks
==13580==    still reachable: 91,012 bytes in 188 blocks
==13580==         suppressed: 0 bytes in 0 blocks

Similarly, when I comment out a call to obx_query_close() and run valgrind on the query-test, it catches a leak of the core resources as well:

==15074== LEAK SUMMARY:
==15074==    definitely lost: 6,200 bytes in 181 blocks
==15074==    indirectly lost: 218,547 bytes in 3,199 blocks
==15074==      possibly lost: 0 bytes in 0 blocks
==15074==    still reachable: 91,012 bytes in 188 blocks
==15074==         suppressed: 0 bytes in 0 blocks

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Therefore, it is clear it can help detect leaks that could be potentially introduced in the future code changes. There is also a load of Warning: set address range perms: large range and mismatched free() / delete / delete [] reports but I don't think those are related to our code, at least for the latter. That would require further investigation though.

Goal

Create a script for project developers and CI. The script:

• compiles all /test/*_test.dart files using dart2native
• executes each compiled test using valgrind
• capture the leak summary and show an error to the user if there is a leak (any non-zero "lost" report)

The script should ideally return a non-zero code in case of an error, so it can easily be used in the CI.