Add numeric normalization strategies

[mattt]

Linked Issue

Alternative to #23

Description

This PR implements JSONEncoder-style numeric strategies on TOONEncoder, adds validation for .throw, updates tests for defaults and custom behavior, and documents the configuration in the README.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Changes Made

^ See description

SPEC Compliance

• This PR implements/fixes spec compliance
• Spec section(s) affected: 3. Encoding Normalization (Reference Encoder)
• Spec version: 3.0.0

Testing

• All existing tests pass
• Added new tests for changes
• Tests cover edge cases and spec compliance

Pre-submission Checklist

• My code follows the project's coding standards
• I have run code formatting/linting tools
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation if needed
• I have reviewed the TOON specification for relevant sections

Breaking Changes

• No breaking changes
• Breaking changes (describe migration path below)

Additional Context

[Copilot]

Pull request overview

This PR adds configurable numeric normalization strategies to TOONEncoder, providing JSONEncoder-style control over how negative zero and non-conforming floating-point values (NaN, Infinity, -Infinity) are encoded. It implements two separate strategies: NegativeZeroEncodingStrategy (normalize or preserve) and NonConformingFloatEncodingStrategy (null, throw, or convertToString). The changes maintain backward compatibility by keeping the default behaviors that match the TOON specification 3.0.

Changes:

• Added NegativeZeroEncodingStrategy and NonConformingFloatEncodingStrategy public enums with associated encoding logic
• Implemented validation function that recursively checks for non-conforming floats when .throw strategy is selected
• Added tests for default behavior, negative zero preservation, and throw strategy
• Updated README documentation with usage examples and updated feature description

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
Sources/ToonFormat/Encoder.swift	Adds two strategy enums, validation function, and encoding logic for numeric normalization
Tests/ToonFormatTests/EncoderTests.swift	Adds tests for new numeric encoding strategies including default behavior and error throwing
README.md	Updates canonical number formatting note and adds new section documenting numeric normalization configuration

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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