v0.7.0

Breaking changes

• Replace file-backed memory mappings with MAP_ANONYMOUS + MADV_HUGEPAGE.
  Allocations now use anonymous mappings with transparent huge page hints instead
  of memory-mapped temporary files. (#67)
• Remove LgAlloc::path, LgAlloc::with_path(), and LgAlloc::file_growth_dampener().
  Use LgAlloc::growth_dampener() instead.
• Remove FileStats, MapStats, and lgalloc_stats_with_mapping().
  lgalloc_stats() is the only stats function.
• Remove LgAllocStats::file and LgAllocStats::map fields.
• Raise minimum size class from 2^10 (1 KiB) to 2^21 (2 MiB), matching one huge page.
• Handle::prefetch now takes a typed element range (prefetch::<T>(Range<usize>))
  and returns PrefetchError instead of AllocError.

Added

• Handle::prefetch::<T>(Range<usize>) for typed prefetch hints via MADV_WILLNEED.
• PrefetchError type for prefetch-specific errors.
• munmap on GlobalStealer::drop to return virtual address space on shutdown.
• Graceful handling of MADV_HUGEPAGE failure (one-time warning instead of error).
• Allocation benchmarks comparing lgalloc, system allocator, and raw mmap.

Fixed

• Use MADV_FREE (Linux) / MADV_DONTNEED (other) for background clear instead of
  MADV_REMOVE, which fails on anonymous memory.

Removed

• numa_maps, memmap2, tempfile, serial_test dependencies.

Other

• Move tests to integration test files.
• Rewrite README with structured sections.
• Update release-plz workflow to patch README version automatically (#68).