feat(mwa-v2): refactor wire protocol, client, and cache for MWA v2

[Zurcusa]

⚠️ NOTE: This is PR 2 of 3 in the MWA v2 stack. Targets pr/3-mwa-v2-types. This refactors the client layer while preserving backward compatibility via [Obsolete] shims (removed in PR #5).

Status	Type	⚠️ Core Change	Issue
Ready	Feature	Yes	Closes #272, partial for #273

Problem

The current MobileWalletAdapterClient uses the v1 MWA wire protocol with flat cluster strings and a simple AuthorizationResultAccounts response shape. It lacks:

• CAIP-2 chain identifier support (#273 item 4)
• Per-account metadata (icon, chains, features, display address)
• Permissive response parsing with size caps for untrusted wallet data
• Authorization caching abstraction (#272)
• DeauthorizeAsync and SignAndSendTransactionsAsync wire methods
• Sign-In With Solana (SIWS) payload support

Solution

Wire protocol (JsonRequest.cs): Add chain, cluster (backward compat), features, sign_in_payload, and sendOptions fields.

Client (MobileWalletAdapterClient.cs): Rewrite with:

• AuthorizeAsync(chain, authToken, features, addresses, signInPayload, ct) — v2 authorize with SIWS
• DeauthorizeAsync(authToken, ct) — async deauthorize with cancellation
• SignAndSendTransactionsAsync(payloads, options, ct) — batch sign-and-send
• CloneAuthorizationAsync(authToken, ct) — clone authorization for multi-session
• Old Authorize/Reauthorize preserved as [Obsolete] shims

Response model (AuthorizationResult.cs): Refactored to v2 shape with List<AccountInfo>, WalletIcon, SignInResult. Shim PublicKey/AccountLabel properties preserved as [Obsolete].

Parser (AuthorizationResponseParser.cs): Permissive parser with size caps (64KB icons, 128-char display addresses, 32 chains max, 16 accounts max) and structured logging gated by LogVerbosity.

Cache (PlayerPrefsAuthorizationCache.cs): Default IAuthorizationCache backed by Unity PlayerPrefs with scoped key support, corrupt-JSON recovery, and legacy key cleanup. Closes #272.

Tests: 9 new EditMode test suites added to Tests/EditMode/ (MwaParser/, MwaCache/, MwaClient/) with 10 JSON fixtures. Updated existing MobileWalletAdapterClientTests for the new API. Added Solana.Unity.Wallet.dll and Solana.Unity.Rpc.dll to the test assembly definition.

Other changes

• Removed XML doc comments from existing test files (cleanup)
• Updated CapabilitiesResult with additional capability fields

Deploy Notes

Backward compatibility: The old Authorize/Reauthorize methods and PublicKey/AccountLabel properties are preserved as [Obsolete] shims. Existing code compiles with deprecation warnings. These shims are removed in PR #5 when the adapter is rewritten.

Testing Matrix

Tested on Pixel 7 emulator and Solana Seeker (real device).

Wallets Tested

Wallet	Networks
Seed Vault (Solana Phone)	DevNet, MainNet
Phantom	DevNet, MainNet
Solflare	DevNet, MainNet
Backpack	MainNet
Jupiter	MainNet

Functionality Coverage

Feature	Emulator (Pixel 7)	Solana Seeker
Login	Passed	Passed
Disconnect	Passed	Passed
Reconnect	Passed	Passed
Deauthorize	Passed	Passed
Sign Transaction	Passed	Passed
Sign All Transactions	Passed	Passed
Sign Message	Passed	Passed
Sign and Send	⚠️ Backpack fails (see PR #5 Known Issue)	⚠️ Backpack fails (see PR #5 Known Issue)
Get Capabilities	Passed	Passed
Sign-In With Solana (SIWS)	Passed	Passed