feat(swift): add Swift SDK implementation

[sammccord]

Description

Add a complete Swift SDK for the Coinbase Developer Platform (CDP). This introduces a new swift/ directory with full EVM and Solana client support, following the same patterns as the existing TypeScript, Python, Go, and Rust SDKs.

Key additions:

• CDPAuth module — JWT-based authentication with EC key parsing and token generation
• CDPSDK module — CdpClient with EvmClient and SolanaClient for account management, signing, and transactions
• OpenAPI integration — Uses swift-openapi-generator for type-safe API client generation
• Auth middleware — Automatically injects JWT auth and correlation headers
• Error handling — Structured CdpError and APIError types
• Examples — 19 runnable examples covering account creation, signing, transactions, and faucet requests for both EVM and Solana
• CI workflows — Lint (swift-format), test, and publish (SPM tag-based) workflows
• Documentation — README, CONTRIBUTING.md, and updated root CONTRIBUTING.md with Swift dev setup and release instructions

Tests

Unit tests added for:

• JWT generation and validation (CDPAuthTests/JWTTests.swift)
• EC key parsing — PEM, hex, and raw formats (CDPAuthTests/KeyParsingTests.swift)
• Auth middleware header injection (CDPSDKTests/AuthMiddlewareTests.swift)
• CdpClient initialization and configuration (CDPSDKTests/CdpClientTests.swift)
• EVM client operations — create, get, list accounts, sign, send (CDPSDKTests/EvmClientTests.swift)
• Solana client operations — create, get, list accounts, sign, send (CDPSDKTests/SolanaClientTests.swift)

Method: swift build + swift test
Platform: macOS (Swift 5.9+)

Output:
Build complete!
Test Suite 'All tests' passed.

Checklist

• Updated the typescript README if relevant
• Updated the python README if relevant
• Added a changelog entry
• Added e2e tests if introducing new functionality

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[sammccord]

closing to extract to separate repo