perf.data validation and hardening (29 patches)

A crafted or corrupted perf.data file can cause out-of-bounds
reads/writes, infinite loops, heap overflows, and segfaults in perf
report, perf script, perf inject, perf timechart, and perf kwork.

This series adds defense-in-depth validation for file parsing:

- Per-event-type minimum size table, enforced before swap and
  processing on both native and cross-endian paths.

- Bounds-checking the one_mmap fast path in peek_event against the
  mapped region size, preventing OOB reads from crafted file_offset.

- Swap handler return values (void -> int) so handlers can propagate
  errors instead of silently corrupting adjacent memory.

- Bounds checking for string fields (null-termination), array counts
  (nr vs payload size), feature section sizes (vs file size), and
  CPU indices (vs nr_cpus_avail / array allocation).

- ABI0 handling for perf_event_attr.size == 0 across all code paths
  (swap, native, synthesize, read_event_desc), with consistent
  behavior regardless of file endianness.

- READ_ONCE() snapshot of event->header.size in process_user_event()
  to prevent compiler rematerialization from MAP_SHARED memory.

- Sanitizer-aware shell test: the truncated perf.data test captures
  stderr and checks for ASAN/MSAN/TSAN/UBSAN markers, since sanitizer
  exits use code 1 which otherwise looks like a clean error exit.

Pre-existing bugs fixed along the way:

- event_contains() macro off-by-one (checked start, not full extent)

- zstd_decompress_stream multi-iteration output.pos bug

- zstd_compress_stream_to_records: broken memcpy fallback -> return -1
  + ZSTD context reset + dst_size underflow guard

- PERF_RECORD_SWITCH sample_id_all offset wrong for non-CPU_WIDE

- cpu_map__from_range any_cpu used as count instead of boolean

- cpu_map__from_mask double-fetch heap overflow (j >= weight guard)

- kwork cpus_runtime BUG_ON with signed comparison

- perf_header__getbuffer64 EOF without errno (silent success)

- read_event_desc ABI0 sentinel (attr.size=0 -> free_event_desc early stop)

- EVENT_UPDATE MASK: missing offsetof underflow guard + pr_warning on
  mask32/mask64 validation paths

Additional pre-existing issues were noticed during review and will be
addressed in follow-up series.

Testing
-------

- perf test at baseline and after the series with 300s timeout -- no
  regressions detected.
- Build with both gcc and clang at every patch.
- checkpatch.pl on all 29 patches.
- perf test on aarch64 (Raspberry PI 4).

Developed with AI assistance (Claude/sashiko), tagged in commits.

Thanks,

- Arnaldo