Check for overflow in StorageView::reserve before allocation

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Summary

• Reject negative reserve requests before the existing capacity fast path.
• Check the element-count-to-byte-count multiplication before allocation, using division to avoid signed overflow.
• Validate before releasing the current buffer, so a rejected request preserves its contents and shape.
• Exercise FLOAT16/FLOAT32 byte-count boundaries, negative sizes, preservation after rejection, and zero/smaller/equal-capacity no-ops.

Validation

Built and tested on macOS arm64, AppleClang 21, Debug, Ruy backend, two build jobs:

cmake -S . -B build -DCMAKE_POLICY_VERSION_MINIMUM=3.5 \
  -DCMAKE_BUILD_TYPE=Debug -DWITH_MKL=OFF -DWITH_ACCELERATE=OFF \
  -DWITH_RUY=ON -DOPENMP_RUNTIME=NONE -DBUILD_TESTS=ON \
  -DBUILD_CLI=OFF -DBUILD_SHARED_LIBS=ON
cmake --build build --target ctranslate2_test --parallel 2
build/tests/ctranslate2_test tests/data \
  '--gtest_filter=StorageViewTest.*:CPU/StorageViewDeviceTest.*'
build/tests/ctranslate2_test tests/data --gtest_brief=1

• Targeted storage tests: 11/11 passed.
• Before the follow-up correction, the same tests against the original Check for overflow in StorageView::reserve byte size #2092 implementation reproduced the negative-size and buffer-preservation failures (9 passed, 2 failed).
• Full local suite: 192 passed, 1 skipped, 3 failed (196 total). The failures are CPU/OpDeviceFPTest.Gemm/float32, GemmBias/float32, and GemmResidual/float32. The same three numerical failures were present in the Check for overflow in StorageView::reserve byte size #2092 baseline before the follow-up correction.
• git diff --check passes. Linux/MKL, CUDA, and Windows have not been tested locally; upstream CI is still needed.

AI assistance disclosure

OpenAI Codex assisted with preparing the follow-up correction and regression tests.

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@jordimas Could you review it when you have a chance?

[jordimas]

@jordimas Could you review it when you have a chance?

Looks good. Thanks for your contribution