Implement Block Scalar support

[bradcypert]

Hey there! Thank you for the library! I am using it in one of my zig projects and noticed that I couldn't parse yaml with block scalars. When the parser encountered these indicators, it would fail with parsing errors.

I implemented basic support for YAML block scalars by:

1. Tokenizer Enhancements (src/Tokenizer.zig)

• Added two new token types: block_literal (|) and block_folded (>)
• Added tokenization rules to recognize these characters as block scalar indicators

2. Parser Implementation (src/Parser.zig)

• Added blockScalar() function to handle block scalar parsing
• Implemented indentation-based content collection
• Added logic to differentiate between literal (preserves newlines) and folded (converts to spaces) styles
• Updated value() function to dispatch to blockScalar() when these tokens are encountered

3. Examples Created

• examples/block_scalars.yml - Simple demonstration
• examples/block_scalar_demo.yml - Comprehensive examples with real-world use cases

Would love it if we can merge this in, but no worries if not! I know this PR came out of the blue (and I'll update my dep to use my fork in the meantime 😄). Thanks again!