Fix JavaDoc code blocks

[andymarek]

This PR fixes JavaDoc code block formatting across the codebase to ensure proper rendering in generated documentation.

Changes

• Replaced legacy JavaDoc {@code ...} blocks with the more reliable <pre><code>...</code></pre> pattern for multi-line code examples
• Converted generic type angle brackets (<>) to HTML entities (<>) to prevent HTML parsing issues in JavaDoc output
• Removed unnecessary curly brace wrappers and @code annotations that were causing formatting inconsistencies
• Applied consistent formatting style to 11 files across the core and mallet modules

Testing

• Executed GitHub Actions

[github-actions]

Code Coverage

Overall Project	98.37%	🍏

Module	Coverage
mallet	99.49%	🍏
core	97.53%	🍏

Files

Module	File	Coverage
mallet	ModelOutputEvaluator.java	100%	🍏
	ConllOutputConfiguration.java	100%	🍏
	MalletCrfTrainer.java	100%	🍏
	ModelOutputConfiguration.java	100%	🍏
	MalletCrfTrainerConfiguration.java	98.74%	🍏
core	TransformingFeatureExtractor.java	100%	🍏
	PatternMatchingFeatureExtractor.java	100%	🍏
	CompositeFeatureExtractor.java	100%	🍏
	Serializables.java	100%	🍏
	InputSequence.java	100%	🍏
	XPathFeatureExtractor.java	93.14%	🍏