integrate v2, add EVM multi-chain support

[Zlerp]

Note

Enables protocol v2 by default with CAIP-2 identifiers and updated HTTP transport, plus flexible network/token support.

• Implement versioned strategies (versions/v1, versions/v2) with new headers (PAYMENT-SIGNATURE, PAYMENT-RESPONSE, PAYMENT-REQUIRED) and CAIP-2 network formatting
• Update controller paywall to support per-endpoint versioning, emit v2 requirement header, match accepts, and set correct response headers; add robust 402 generation
• Add multi-chain acceptance via config.accept and per-accept wallet addresses; refactor requirement generation to output v1/v2 formats
• Add custom EVM chain/token registration and CAIP-2 conversion helpers; extend chains with Solana (incl. fee payer) and adjust validator to handle Solana transactions
• Revise PaymentPayload/PaymentRequirement to v2 shapes (amount, nested accepted, top-level resource) while keeping v1 compatibility
• Bump gem to 1.0.0; update README, CHANGELOG, initializer, and tests to cover new behaviors

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[Copilot]

Pull request overview

This PR integrates x402 protocol v2 with significant architectural changes to support multi-chain payments, CAIP-2 network identifiers, and a version strategy pattern. The default protocol version is now v2, with backward compatibility for v1 maintained through a strategy pattern.

Key changes:

• Implements version strategy pattern (V1, V2) with protocol-specific headers, network formats, and requirement structures
• Adds multi-chain payment support via config.accept() allowing simultaneous acceptance of payments on multiple chains
• Introduces custom chain and token registration for EVM networks beyond built-in options
• Updates PaymentRequirement and PaymentPayload to handle both v1 and v2 formats with CAIP-2 network normalization

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
spec/x402/versions/v2_spec.rb	Comprehensive tests for v2 strategy: CAIP-2 formatting, PAYMENT-SIGNATURE header, amount field usage
spec/x402/versions/v1_spec.rb	Tests for v1 legacy strategy: internal network format, X-PAYMENT header, maxAmountRequired field
spec/x402/requirement_generator_spec.rb	Tests for multi-version requirement generation, multiple accepts, Solana support, and version overrides
spec/x402/configuration_spec.rb	Tests for custom chain/token registration, multi-chain accept configuration, and effective_accepted_payments
spec/x402/chains_spec.rb	Tests for CAIP-2 mapping, custom chains, token configuration, and asset address resolution
lib/x402/versions/v2.rb	V2 strategy implementation with CAIP-2 formatting, new headers, and v2-specific requirement structure
lib/x402/versions/v1.rb	V1 legacy strategy with internal network format and original header names
lib/x402/versions/base.rb	Abstract base class defining version strategy interface
lib/x402/versions.rb	Factory method for version strategy instantiation
lib/x402/requirement_generator.rb	Updated to support multi-chain accepts, version-specific formatting, and Solana fee payer handling
lib/x402/rails/controller_extensions.rb	Enhanced paywall logic with version-aware headers, network matching, and requirement generation
lib/x402/payment_requirement.rb	Added version-aware to_h method, CAIP-2 network normalization, and max_amount_required alias
lib/x402/payment_payload.rb	Extended for v2 with accepted/resource_info fields, network normalization, and version-specific serialization
lib/x402/configuration.rb	Added accept(), register_chain(), register_token() methods and version/fee_payer configuration
lib/x402/chains.rb	Extended with Solana chains, CAIP-2 mapping, custom chain support, and fee payer configuration
lib/x402/rails/version.rb	Bumped version to 1.0.0 for v2 protocol support
lib/x402/rails/generators/templates/x402_initializer.rb	Updated default facilitator URL to include www subdomain
README.md	Added extensive documentation for v2 features, custom chains/tokens, multi-chain accepts, and protocol versions
CHANGELOG.md	Documents v2 integration, multi-chain support, and breaking changes
Gemfile.lock	Updated to reflect new gem version 1.0.0

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