fix incorrect types of pointers

[ferjakub]

1/ isolate_handle.cc:

snapshot.data, which is allocated by V8 as new char[] (snapshot.cc:546) is owned by snapshot_data_ptr, which is of type unique_ptr<const char> => delete is called upon destruction, delete[] should be called instead

=> changed the type of the unique_ptr to reflect this

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2/ scheduler.cc:

uv_async is allocated as uv_async_t (128 B) but deleted as uv_handle_t (96 B)

=> added a cast back from uv_handle_t* to uv_async_t* before deleting

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Technically, these situations are UB, but practically they don't cause any issues. They came up as a result of running the test suite with ASan which doesn't complain anymore after this trivial fix.

[laverdet]

Thanks!