Environment is copyable but owns a raw Grid*, so copying it double-deletes the grid

[dmccoystephenson]

Environment owns a heap-allocated Grid through a raw pointer — grid = new Grid(id, size) in the constructor (src/environment.cpp:10) and delete grid in the destructor (src/environment.cpp:14) — but declares no copy constructor or copy-assignment operator (src/header/environment.h:14-15 declare only the constructor and destructor). The compiler therefore generates a shallow copy: two Environment objects end up holding the same Grid*, and the second one to be destroyed deletes an already-freed grid.

This is the same class of defect as #27 (a new/free mismatch in the destructor, fixed in #30): the destructor is now correct, but the object is still unsafe to copy. Any of the following triggers a double delete at scope exit:

Environment a(0, "Earth", 4);
Environment b = a;          // copy-construct: b.grid == a.grid

Environment a(0, "Earth", 4);
Environment b(1, "Mars", 4);
b = a;                      // copy-assign: b's original grid is leaked, then a.grid is deleted twice

Passing an Environment by value to a function, or storing one in a std::vector<Environment> that reallocates, does the same. Nothing in the current test suite copies an Environment, so the suite does not observe it, but run_tests_asan.sh would report it as a heap-use-after-free / double-free the moment such a test were added.

Suggested fix: delete the copy operations in the header, matching the existing Grid() = delete; style already used in src/header/grid.h:

Environment(const Environment&) = delete;
Environment& operator=(const Environment&) = delete;

This turns the runtime double-free into a compile error for any caller that copies. (Alternatively, Grid* grid could become std::unique_ptr<Grid>, which gives the same non-copyable semantics and removes the explicit delete; either approach is acceptable, the deleted-copy pair being the smaller change.) A characterization test cannot assert a compile error, so the acceptance criterion is a clean bash run_tests_asan.sh run plus the two deleted declarations being present in the header.

This issue body was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson