[Feature] New validation rule: pipe

[zlooun]

Summary

• Core: add pipe as a built-in rule (JS implementation, registration in validator, full type definitions).
• Docs: new README section for pipe, including nested pipe (tree) example and validate → transform → validate flow.
• Tests: JS/TS unit tests for pipe covering nested pipelines, early halt on inner errors, and string → number conversion before re-validation.

Why

Enables composable, sequential validation/sanitization pipelines without custom glue code—validate raw input (e.g., string), parse/transform it, then validate the transformed value (including nested schemas) while preserving required/nullable semantics and short-circuiting on errors. Reduces boilerplate for multi-step validation and makes tree-like pipelines first-class.

Testing

• npm test (includes TS suite)

[zlooun]

@icebob can u review pls?😁