feat(stdlib): add validation library (#20)

[bastitva0-blip]

PR Body

Description

This PR implements the feature request outlined in #20, introducing the std.lib.validation standard library module for ProXPL. It provides a robust, declarative, and chainable API for schema-based data validation and quick runtime data validation checks, perfectly matching the language's "batteries included" philosophy.

This library operates entirely in userland ProXPL using core built-ins, introducing zero overhead or modifications to the native C/C++ core engine.

Related Issues

Closes #20

Proposed Changes

• Core Validator Engine (std/lib/validation.prox): Implements chainable rules for string(), number(), bool(), list(), and any() types.
• Schema Contract Evaluator: Implements Schema.define() and schema.validate() to parse payloads and return complete, structured ValidationResult objects with accumulated error lists rather than failing early.
• Inline Utility Functions (Validate.*): Adds quick, standalone convenience methods (e.g., Validate.isEmail, Validate.isInRange) for minor runtime assertions.
• Comprehensive Test Suite (tests/test_validation.prox): Thoroughly tests edge cases, validation boundaries, and nested type evaluation.
• Documentation & Visibility: Added full API documentation in docs/stdlib/validation.md and updated std/README.md and CHANGELOG.md.

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File Statistics & Changes

docs/stdlib/validation.md   |  (New API Reference & Examples)
std/lib/validation.prox     |  (Core Library Implementation)
tests/test_validation.prox  |  (Integration & Unit Tests)
CHANGELOG.md                |  +13 lines
std/README.md               |  +23 lines
Checklist:
[x] I have read the CONTRIBUTING.md guidelines.

[x] Code follows the language standards and formatting conventions (CODING_STANDARD.md).

[x] All functionalities are fully covered by tests in tests/test_validation.prox.

[x] Documentation has been updated accordingly.

Maintainer Notes / Open Design Choices
To address the initial questions raised in the feature proposal:

Error Formatting: The library uses structured ProXPL Dictionaries { field: string, message: string } within the ValidationResult.errors list to keep serialization simple, avoiding heavy object overhead.

Type Checking: Strict type checking is enforced using the built-in type_of() method rather than completely generic duck typing to prevent silent mis-evaluations.

[bastitva0-blip]

yeah take your time please free to tag me and discuss about this

[ProgrammerKR]

Thanks for the contribution and the comprehensive documentation.

This is a substantial addition to the standard library, so I'll take some time to review the implementation, API design, tests, and documentation before making a decision.

I also noticed the Windows CI failure again. Since this has occurred on multiple PRs, I'll verify whether it's a repository/CI issue or something introduced by this change.

I'll update you after the review. Thanks for your patience!

[bastitva0-blip]

@ProgrammerKR
Hey, did some research on the Windows CI failure : this is a well-known upstream issue, not specific to this repo.

Root Cause

The official LLVM Windows installer and Chocolatey package don't ship LLVMConfig.cmake or llvm-config.exe, which is what CMake's find_package(LLVM) needs. This is a documented and longstanding LLVM issue. The current setup_llvm_windows.ps1 script tries to work around it but hits a dead end because the file simply isn't there.

This also explains why the Windows runner itself recently dropped llvm-config.exe from C:\Program Files\LLVM\bin entirely.

Fix

Replace the custom PowerShell script with KyleMayes/install-llvm-action, which is specifically built to solve this problem and is widely used by compiler projects on GitHub Actions.

In .github/workflows/*.yml, replace the Set up LLVM (Windows) step with:

- name: Install LLVM and Clang
  if: matrix.os == 'windows-latest'
  uses: KyleMayes/install-llvm-action@v2
  with:
    version: "17"

- name: Set LLVM_DIR (Windows)
  if: matrix.os == 'windows-latest'
  shell: pwsh
  run: |
    echo "LLVM_DIR=${{ env.LLVM_PATH }}/lib/cmake/llvm" >> $env:GITHUB_ENV
    echo "CMAKE_PREFIX_PATH=${{ env.LLVM_PATH }}" >> $env:GITHUB_ENV

After this, scripts/setup_llvm_windows.ps1 can be removed entirely.

This is unrelated to any code changes in this PR — the same failure appears on PR #22 which only touched 3 lines of C with no new files.

[ProgrammerKR]

@bastitva0-blip Thanks for investigating and sharing the root cause.

Could you please create a separate issue for this Windows CI/LLVM setup problem with the details and proposed solution? I'll assign it to you.

If you'd like to work on it, feel free to submit a PR to fix it. Otherwise, I'll take care of implementing the fix myself.

Thanks again for your contribution and the detailed research!