Comprehensive logging system to eliminate unwanted console output (Issue #84)

[krystophny]

Summary

• Implements comprehensive logging system to replace all unwanted console output
• Adds configurable log levels for production, development, and debugging use
• Provides clean library interface with zero output by default in production
• Maintains backward compatibility while giving users full control over verbosity

Technical Implementation

New Logging Module (fortplot_logging.f90)

! User interface for log level control
call set_log_level(LOG_LEVEL_SILENT)    ! Zero output for production
call set_log_level(LOG_LEVEL_WARNING)   ! Default: errors + warnings only  
call set_log_level(LOG_LEVEL_INFO)      ! Verbose: includes success messages
call set_log_level(LOG_LEVEL_DEBUG)     ! Maximum verbosity for debugging

Console Output Cleanup

Replaced 35+ print statements across multiple modules:

Production Library Files:

• fortplot.f90: Unimplemented feature errors → log_error()
• fortplot_png.f90: Success/failure messages → log_info()/log_error()
• fortplot_pdf.f90: File creation confirmations → log_info()
• fortplot_text.f90: Font initialization errors → log_error()
• fortplot_figure_core.f90: User prompts and warnings → log_info()/log_warning()
• fortplot_raster.f90: Backend usage errors → log_error()

Animation/3D Graphics:

• fortplot_animation.f90: Progress and error messages → appropriate log levels
• fortplot_gltf.f90: File creation confirmations → log_info()
• fortplot_ascii.f90: Terminal plot saves → log_info()

User Experience Impact

Before (Issue #84)

use fortplot
call figure(800, 600)
call plot(x, y)
call savefig('plot.png')
! Output: "PNG file 'plot.png' created successfully!"
! Cannot be silenced - reduces library usability

After (This PR)

use fortplot
call set_log_level(LOG_LEVEL_SILENT)  ! Production mode
call figure(800, 600)
call plot(x, y)
call savefig('plot.png')
! Output: (nothing) - clean production experience

Development Mode

use fortplot
call set_log_level(LOG_LEVEL_INFO)    ! Development mode
call figure(800, 600)
call plot(x, y)
call savefig('plot.png')
! Output: "[INFO] PNG file 'plot.png' created successfully!"

Test Plan

• Silent Mode Test: Verify zero console output in LOG_LEVEL_SILENT
• Level Filtering Test: Verify each log level shows appropriate messages
• Backward Compatibility: Existing code works with default warning level
• Production Integration: Library can be used in applications without unwanted output
• Error Visibility: Critical errors still visible at appropriate log levels

Validation

# Test silent operation  
fpm test --target test_silent_output

# Test logging level control
fpm test --target test_logging_system

# Verify library still functions normally
fpm build && fpm test

Benefits

✅ Clean Production Use: Zero unwanted output with LOG_LEVEL_SILENT
✅ Developer Friendly: Configurable verbosity for debugging
✅ Backward Compatible: Default behavior preserves warnings/errors
✅ Consistent Interface: Unified logging across all library modules
✅ User Control: Applications decide their own output preferences

Fixes #84 - Console output statements in production code reduce library usability

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 76.00000% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/fortplot_animation.f90	20.00%	8 Missing ⚠️
src/fortplot_figure_core.f90	25.00%	6 Missing ⚠️
src/fortplot.f90	50.00%	4 Missing ⚠️
src/fortplot_gltf.f90	50.00%	2 Missing ⚠️
src/fortplot_text.f90	0.00%	2 Missing ⚠️
src/fortplot_png.f90	50.00%	1 Missing ⚠️
src/fortplot_raster.f90	0.00%	1 Missing ⚠️

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