Add test for external_pointer attribute preservation and fix move assignment operator

[Copilot]

Issue #308 reported that moving an external_pointer clears its attributes. The fix was already applied (changing move operations to transfer data_ directly instead of calling reset(rhs.release())), but lacked test coverage and had a critical bug.

Changes

• Added test case for attribute preservation during move operations (both move constructor and move assignment operator)
• Fixed missing return statement in external_pointer::operator=(external_pointer&&) - the operator was declared to return external_pointer& but had no return, causing undefined behavior

Test Example

// Move constructor preserves attributes
cpp11::external_pointer<int> p(new int(42));
Rf_setAttrib(p, R_ClassSymbol, Rf_mkString("test_class"));

cpp11::external_pointer<int> p_moved = std::move(p);
// Attribute is preserved on p_moved

// Move assignment operator preserves attributes  
cpp11::external_pointer<int> p1(new int(1));
Rf_setAttrib(p1, R_ClassSymbol, Rf_mkString("test_class"));

cpp11::external_pointer<int> p2(nullptr);
p2 = std::move(p1);
// Attribute is preserved on p2

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[Copilot]

Pull request overview

This PR fixes a critical bug in the external_pointer move assignment operator and adds comprehensive test coverage for attribute preservation during move operations, addressing issue #308.

Changes:

• Added missing return statement in external_pointer::operator=(external_pointer&&) to fix undefined behavior
• Added test case verifying attributes are preserved during both move construction and move assignment
• Added CodeQL configuration file

Reviewed changes

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

File	Description
inst/include/cpp11/external_pointer.hpp	Fixed move assignment operator by adding missing return statement
cpp11test/src/test-external_pointer.cpp	Added comprehensive test for attribute preservation in move operations
_codeql_detected_source_root	Added CodeQL source root configuration

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[Copilot]

Calling delete on the result of release() will attempt to delete the memory that was already wrapped by the external pointer, but the external pointer's finalizer has already been set up to delete this memory when the R object is garbage collected. This creates a double-free scenario. Since the external pointer owns the memory, simply allowing p_moved to go out of scope is sufficient - the finalizer will handle cleanup.

[Copilot]

Same double-free issue as above. The external pointer's finalizer will delete the memory when the R object is garbage collected. Calling delete on release() creates a double-free scenario. Remove this manual deletion and let the external pointer's destructor handle cleanup.