#3385 [Engine] avoid hanging on PleReader initialization failures

说明

## Problem and result

On current upstream main, `PleReader::open()` still hangs during cleanup if read-buffer allocation fails or if a reader is reopened with a table range beyond EOF. The failed `open()` never returns its existing error. After this change, it closes cleanly and a later valid open/read succeeds.

## Related discussion

Retested the report in [#3045](https://github.com/Niko1221/Strata/issues/3045), which was closed during the 0.2.0-beta tracker reset. The original PR [#3046](https://github.com/Niko1221/Strata/pull/3046) was also closed in that reset.

## Approach

Publish the in-flight slot count only after the buffers and free-slot list are ready, and reset the count when closing. Add Linux CPU-only lifecycle coverage for normal reads, failed reopen, and injected allocation failure in caller-thread and I/O-worker modes. The allocation failure uses link-time `posix_memalign` wrapping and does not add production fault-injection behavior.

## Validation

Linux x86_64, GCC 14.2.0, CUDA 13.4.92, NVIDIA RTX 4070 Ti SUPER; base revision `e88ee39d1d6be6e3364183af3b39b62a7ed6f211`, candidate revision `9f4b65fc`.

**Passed:**
- CPU: `cmake -S . -B build/ple-reader-beta -DSTRATA_BUILD_TESTS=ON -DSTRATA_WERROR=ON`; `cmake --build build/ple-reader-beta --target ple_reader_lifecycle_test direct_file_async_test -j2`; and `ctest --test-dir build/ple-reader-beta --output-on-failure -R '^(ple_reader_(reads|reopen|alloc)_(caller|threaded)|direct_file_async_test)$'`: targets built and all 7 tests passed.
- CUDA: `cmake -S . -B build/ple-reader-cuda -DSTRATA_BUILD_TESTS=ON -DSTRATA_WERROR=OFF -DSTRATA_ENABLE_CUDA=ON -DCMAKE_CUDA_COMPILER=/usr/local/cuda-13.4/bin/nvcc`; `cmake --build build/ple-reader-cuda --target strata ple_reader_lifecycle_test direct_file_async_test -j2`: all targets built.
- CUDA CTest: `ctest --test-dir build/ple-reader-cuda --output-on-failure -R '^(ple_reader_(reads|reopen|alloc)_(caller|threaded)|direct_file_async_test)$'`: all 7 tests passed.
- Reproduced on unchanged base revision `e88ee39d`: both read controls passed; `reopen` and injected `alloc` cases timed out after 2 seconds in caller and threaded modes (4 hangs).
- `git diff --check origin/main...HEAD`: passed.

**Failed:**
- With `STRATA_WERROR=ON`, the CUDA build command `cmake --build build/ple-reader-cuda --target strata ple_reader_lifecycle_test direct_file_async_test -j2` stopped on `-Werror=misleading-indentation` in unchanged `src/core/layer.cpp`. The CUDA build passed with WERROR disabled; warnings are outside this change.

**Not run:**
- HIP and SYCL builds: `hipcc`, `dpcpp` and `icpx` are unavailable.
- Windows runtime checks and real model inference.

## Limits

The reproduction uses a synthetic file and real DirectFile I/O on Linux; it verifies initialization and recovery behavior, not a production memory-pressure incident or model inference.