feat: add Stellar wallet support

[tysonwil]

Problem

Para Swift SDK did not expose Stellar as a wallet type or provide the small Stellar payload/address helpers needed for apps to create, display, and sign with Stellar wallets through the existing bridge.

Solution

• Add STELLAR wallet/external-wallet type support.
• Add Stellar G-address derivation from Ed25519 public keys and Solana-style base58 addresses.
• Add minimal Stellar transaction/memo/network models that encode into the existing bridge signing path.
• Add focused XCTest coverage for wallet decoding, transaction payload encoding, and address derivation vectors.

Verification

• xcodebuild -workspace /Users/tyson/para/ParaSwift.xcworkspace -scheme ParaSwift -sdk iphonesimulator -configuration Release build
• xcodebuild -workspace /Users/tyson/para/ParaSwift.xcworkspace -scheme ParaSwift -sdk iphonesimulator -destination "platform=iOS Simulator,name=iPhone 17,OS=26.5" test
• swift test is not viable for this package on macOS because the SDK imports UIKit.
• swiftformat . was not run because swiftformat is not installed locally.

Companion PRs

• Swift example: https://github.com/capsule-org/js-monorepo/pull/1778
• Flutter SDK: https://github.com/capsule-org/flutter-sdk/pull/81
• Flutter example: https://github.com/capsule-org/js-monorepo/pull/1772

Notes

Core JS Stellar support already exists from js-monorepo PR #1545 / commit 648f5bb55.

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[chatgpt-codex-connector]

Preserve existing Stellar addresses

When a Stellar wallet has no publicKey and address is already a Stellar G-address (the shape used in the new wallet decoding test), this fallback tries to decode that G-address as a Solana/base58 public key. Stellar strkeys are base32/checksummed and many contain characters not in base58, or decode to the wrong byte length, so wallet.stellarAddress returns nil for an otherwise valid Stellar wallet instead of exposing its usable address.

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