Release 3.0.3

Changes from 3.0.2 to 3.0.3

• Harden frame parsing against malformed trailer lengths, invalid metalayer
  offsets and lengths, and lazy-chunk compressed sizes that extend past the
  end of a frame. This prevents invalid offset computation,
  out-of-bounds reads, and a double-free on malformed inputs. Thanks to
  @metsw24-max.

• Fix integer-overflow paths in b2nd chunk-size and slice-buffer
  calculations that could otherwise lead to heap corruption or invalid
  allocations. Thanks to @metsw24-max.

• Improve stdio and mmap I/O safety by validating NULL streams, file sizes,
  offsets, and integer conversions, and by tightening cleanup/error paths.
  Thanks to @metsw24-max.

• Replace unsafe string formatting/concatenation in compressor listing,
  codec-version reporting, directory helpers, and frame path handling with
  bounded operations and allocation checks. Thanks to @metsw24-max.

• Validate negative indices in offset reordering to reject malformed offset
  tables more reliably. Thanks to @uwezkhan .

• Add regression tests covering malformed frame trailer/metalayer data,
  lazy-chunk bounds, b2nd chunk-size overflows, stdio validation, mmap error
  handling, and negative reorder offsets.