Refactor specialized decompression offset handlers with macros (#372)

Replaced repetitive implementations of `decompress_offset_3` through `decompress_offset_15` with `decompress_offset_rotated` and `decompress_offset_simple` macros. This reduces code duplication and standardizes the tail copy logic to use a safe temporary buffer, resolving potential overlapping copy issues in offset 12, 14, and 15 handlers.

Refactored `src/decompress/x86.rs` to use new macros. Verified with existing offset tests.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: 404Setup