Improve openpdf-renderer: documentation, build config, and code quality

[Copilot]

Description of the new Feature/Bugfix

Modernizes the openpdf-renderer module with production-ready improvements:

Documentation

• README.md: Added feature matrix, complete working examples with imports, Maven dependency snippet, troubleshooting guide, and supported PDF features table
• Package documentation: Created package-info.java for org.openpdf.renderer, colorspace, and font packages with API overviews

Build Configuration

• pom.xml: Added Javadoc plugin (generates API docs) and Source plugin (attaches sources to releases), expanded project description

Code Quality

• CMYKColorSpace.java: Removed 5 System.out/err debug statements
• BuiltinFont.java: Removed 2 System.out/err debug statements
• TrueTypeFont.java: Fixed toString() to use StringBuffer instead of printing to System.out (actual bug)

Example of improved README usage section:

ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
PDFFile pdf = new PDFFile(buf);
PDFPage page = pdf.getPage(1);  // 1-based index

Rectangle rect = new Rectangle(0, 0,
    (int) page.getBBox().getWidth(),
    (int) page.getBBox().getHeight());

Image img = page.getImage(rect.width, rect.height, rect, null, true, true);

Unit-Tests for the new Feature/Bugfix

• Unit-Tests added to reproduce the bug
• Unit-Tests added to the added feature

N/A - Documentation and code quality improvements only, no functional changes.

Compatibilities Issues

None. No breaking changes, no method signature modifications.

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Testing details

Changes are documentation and cleanup only. Verified:

• Code review: No issues
• CodeQL scan: No vulnerabilities
• All modified files maintain valid Java syntax

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud