Add .gitignore and .gitattributes for repo hygiene.

[gustavofreze]

Prevent agent/IDE folders (.claude, .idea, .vscode) from being versioned and exclude dev-only files (tests, phpstan, phpcs, phpunit configs) from the Packagist tarball via export-ignore.

[Copilot]

Pull request overview

This PR improves repository hygiene and packaging by adding ignore/export rules and tightening up developer tooling/configuration to keep dev-only artifacts out of version control and Packagist exports.

Changes:

• Add/expand .gitignore, .gitattributes, and .editorconfig to normalize line endings and ignore local/dev artifacts.
• Update Composer dev dependencies/scripts and Make targets to support composer-normalize and new helper commands.
• Refresh CI artifact action versions and update library description/documentation to match the enum-based currency model.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
phpstan.neon.dist	Removes unused ignoreErrors key from PHPStan config.
infection.json.dist	Tweaks Infection mutators configuration.
composer.json	Normalizes metadata, updates dev dependencies, plugin allow-list, and script ordering.
README.md	Updates Overview text to reflect enum-based ISO-4217 modeling and fraction digits.
Makefile	Adds composer normalize to configure, adds show-outdated, clarifies test-file usage, updates help output.
.gitignore	Expands ignores to cover common IDE/agent folders and build/test artifacts.
.github/workflows/ci.yml	Updates artifact action versions and removes explicit bcmath extension installation.
.github/copilot-instructions.md	Adds Copilot guidance pointing to .claude/ instruction sources.
.gitattributes	Adds LF normalization and export-ignore list to exclude dev-only files from Packagist tarballs.
.editorconfig	Adds baseline formatting conventions for the repo.
.claude/rules/php-library-testing.md	Adds PHPUnit/BDD conventions and mutation/coverage rules for agent guidance.
.claude/rules/php-library-modeling.md	Adds modeling/architecture rules for library structure.
.claude/rules/php-library-documentation.md	Adds documentation standards for Markdown files.
.claude/rules/php-library-code-style.md	Adds semantic PHP code-style rules for agent guidance.
.claude/rules/github-workflows.md	Adds workflow authoring rules for agent guidance.
.claude/CLAUDE.md	Adds project context, command list, and formatting rules for agent guidance.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.