Port TypeScript additional info handlers, image resources, and descriptor modules to Rust

- descriptor.rs: Complete descriptor parsing/writing implementation
  - All OSType value types (doub, long, bool, enum, obj, VlLs, etc.)
  - Reference structure handling
  - Unit value support (Pixels, Angle, Percent, etc.)
  - Version and descriptor reading/writing
  - Comprehensive roundtrip tests

- image_resources.rs: Image resource handlers
  - Resolution info (1005)
  - XMP metadata (1060), caption digest (1061)
  - Print information and flags (1011, 1082)
  - Background color (1010), copyright (1034), URL (1035)
  - Grid and guides (1032)
  - Global angle (1037), altitude (1049)
  - Layer state (1024), groups (1026), selection IDs (1069)
  - Alpha names (1006, 1045), identifiers (1053)
  - ICC profile (1039), print scale (1062)
  - Generic resource read/write framework
  - Roundtrip tests for major resources

- additional_info.rs: Layer additional info handlers
  - Unicode layer name (luni), layer ID (lyid)
  - Layer color (lclr), section divider (lsct/lsdk)
  - Blend flags (clbl, infx, knko)
  - Protected flags (lspf), name source (lnsr)
  - Text layer data (TySh) with transform and descriptors
  - Vector fill (SoCo, GdFl, PtFl)
  - Vector stroke (vscg, vstk)
  - Vector mask (vmsk/vsms) with bezier paths
  - Layer effects (lrFX, lfx2)
  - Placed layer/smart objects (PlLd, SoLd)
  - Artboard data (artb, artd)
  - Metadata (shmd, cust)
  - Unknown section preservation
  - Roundtrip tests for core handlers

- reader.rs/writer.rs extensions:
  - read_color/write_color for Color types
  - read_fixed_point_32/write_fixed_point_32
  - read_fixed_point_path_32/write_fixed_point_path_32
  - Helper methods for descriptor and resource parsing

All tests passing (20/20)

Co-authored-by: ioma8 <6624752+ioma8@users.noreply.github.com>

Author: Copilot