Add test for flatbuffers array header

[paulquiring]

Add test for flatbuffers/array.h.

[github-actions]

The created documentation from the pull request is available at: docu-html

[Copilot]

Pull request overview

This PR adds GoogleTest coverage for the upstream FlatBuffers C++ headers used by score/flatbuffers, specifically targeting flatbuffers/array.h and flatbuffers/allocator.h, and wires the new tests into the Bazel cc_test target.

Changes:

• Add comprehensive unit/fault-injection tests for flatbuffers/array.h APIs and specializations.
• Add interface/fault-injection tests for flatbuffers/allocator.h, including Allocator::reallocate_downward.
• Fix and expand score/flatbuffers:flatbuffers_cpp_library_test sources in score/flatbuffers/BUILD.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 5 comments.

File	Description
score/flatbuffers/details/flatbuffers_array_test.cpp	New test suite covering flatbuffers::Array behaviors (casts, iteration, spans, mutation, CopyFromSpan, specialization/death tests).
score/flatbuffers/details/flatbuffers_allocator_test.cpp	New test suite validating flatbuffers::Allocator contract and default reallocate_downward behavior (including fault paths).
score/flatbuffers/BUILD	Updates flatbuffers_cpp_library_test to use the correct allocator test filename and adds the new array tests.

Suppressed comments (3)

score/flatbuffers/details/flatbuffers_array_test.cpp:664

• This downcast is undefined behavior: CastToArray(raw) does not produce an ArrayTestAccess<T,N> object, so static_casting the base reference to the derived type is invalid. Use an explicit reinterpret_cast overlay if you need to call the protected overloads.

    auto& accessor = static_cast<ArrayTestAccess<int32_t, 3>&>(CastToArray(raw));

score/flatbuffers/details/flatbuffers_array_test.cpp:683

• This downcast is undefined behavior: CastToArray(raw) does not produce an ArrayTestAccess<T,N> object, so static_casting the base reference to the derived type is invalid. Use an explicit reinterpret_cast overlay if you need to call the protected overloads.

    auto& accessor = static_cast<ArrayTestAccess<Point, 2>&>(CastToArray(raw));

score/flatbuffers/details/flatbuffers_array_test.cpp:756

• This reinterpret_cast assumes the byte buffer is suitably aligned (and large enough) for Array<Offset, 2>. Use alignas + sizeof(Array<...>) to avoid misalignment/size-related UB.

    uint8_t buf[2] = {0};
    const auto& arr = *reinterpret_cast<const Array<Offset<void>, 2>*>(buf);
    EXPECT_DEATH({ arr[0]; }, "");

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