chore: optimization patches and refactoring

[swagfin]

• Bumped the library to 8.0.0.
• Introduce faster rendering with improved caching and prepared expressions.
• Add reusable compiled templates and direct TextWriter output.
• Support nested loops and conditions.
• Add validation, strict mode, cancellation, and execution limits.
• Add optional lazy property access and streaming aggregates.
• Fix placeholder collisions, nullable conditions, numeric precision, and date formatting.
• Refresh the README with practical examples.
• Modernize test tooling, add benchmarks, and expand coverage to 170 passing tests.