Validate note accessor bounds

[sstamenk]

Fix note indexing and record validation in the section and segment accessors. The index check used the section's byte size instead of the number of parsed notes.

Changes

• Share record decoding between scanning and retrieval, and revalidate cached offsets against the current data.
• Use memcpy, byte-order conversion, and widened padding calculations to validate the complete record.
• Require terminated owner names while preserving nameless notes. Leave output parameters unchanged when validation fails.

The public API is unchanged.

Tests

Eight scenarios run across ELF32/ELF64 and both byte orders. Coverage includes invalid indices, truncated and oversized records, owner names, data mutation, serialized sections/segments, and unaligned headers.

• Full suite: 105/105 passed with MSVC ASan.
• Focused note tests: 32/32 passed with GCC ASan/UBSan.

Prepared with AI assistance.