refactor: split fortplot_raster.f90 to comply with file size limits #360
Description
Problem
During PR #359 review, identified that fortplot_raster.f90 exceeds the QADS hard limit of 1000 lines per file.
Current Status: 1137 lines (137 lines over limit)
Required Action
Split fortplot_raster.f90 into smaller, focused modules following Single Responsibility Principle (SRP).
Suggested Approach
- Extract bitmap operations to
fortplot_bitmap.f90 - Extract PNG encoding to
fortplot_png_encoder.f90 - Keep core raster operations in main module
Priority
MAJOR - Violates QADS file size standards but doesn't block current functionality
Found during code quality review of PR #359.