fix(cutile): validate full tensor shapes before allocation

[uurl]

Closes #1451

api::full currently uses unchecked multiplication to calculate its flattened element count. Invalid shapes can panic during construction or wrap before allocation and initialization, with shape validation occurring later during reshape.

Validate the element count with checked multiplication and reject zero dimensions and flattened lengths above i32::MAX. Invalid inputs return DeviceError::Internal when the operation executes, before GPU allocation or kernel execution. zeros and ones inherit the validation through full.

Add five host tests and three GPU tests covering overflow, zero dimensions, the i32 boundary, construction without panics, and valid tensor shapes and values. Preserve scalar shape [].

Validation

Run from cutile-rs:

cargo fmt --all -- --check
git diff --check
cargo test -p cutile --lib api::full_shape_tests
cargo test -p cutile --release --lib api::full_shape_tests
cargo test -p cutile --test gpu tensor_guards::full_
cargo test -p cutile --release --test gpu tensor_guards::full_
cargo clippy -p cutile --lib --test gpu -- -D warnings
RUST_TEST_THREADS=1 bash scripts/run_all.sh

All commands passed. The serial full run passed CPU and GPU tests, 24 examples, and all eight benchmark smoke tests. Three examples were skipped because they require newer Tile IR versions.

The default parallel run failed in warmup_composed::composed_builder_compile_terminal_warms_the_dispatched_specialization, with a JIT compile count of 17 instead of 18. That test passed in isolation, and all 16 warmup_suite tests passed serially. These results suggest a cache state or test ordering dependency; no warmup code is changed in this PR.

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