Feat: enable signAllTransactions for Ingame & External walllets

[owais-star]

⚠️ NOTE: This PR introduces significant improvements to transaction signing, particularly SignAllTransactions, across wallets. Additionally, deprecated and unmaintained Phantom-specific integration has been removed as part of a refactor. Ensure compatibility with your project's transaction flow and update your code if it relied on Phantom WebGL integration.

Status	Type	⚠️ Core Change	Issue
Ready	Feature/Refactor	Yes	Link

Problem

The current implementation of SignAllTransactions in the Solana.Unity-SDK is incomplete and inefficient, causing issues when signing multiple transactions simultaneously. Additionally, the SDK contains redundant code paths, including outdated Phantom wallet integration that is no longer maintained.

Solution

This PR enhances the SignAllTransactions method by:

• Allowing multiple transactions to be signed more efficiently across wallets.
• Adding deduplication of transaction signatures to prioritize non-empty signatures.
• Improving transaction deserialization for both VersionedTransaction and Transaction types, making it more robust for different transaction versions.

Additionally, as part of a refactor:

• Phantom-specific integration (WebGL and mobile) has been removed due to its deprecated status and lack of maintenance, consolidating wallet logic across platforms.

Before & After Screenshots

BEFORE:
Inefficient handling of multiple transactions in SignAllTransactions

AFTER:
Improved SignAllTransactions method with efficient handling of multiple transactions and signature validation

Other changes (e.g. bug fixes, small refactors)

• Deprecated Phantom wallet-specific code paths were removed to clean up and simplify wallet integration logic.
• Introduced the GetSignatureForAddress method to retrieve signatures for specific public keys.
• Refined error handling for wallet connection failures.

Deploy Notes

This PR introduces breaking changes by removing the Phantom-specific wallet integrations. Projects relying on Phantom in WebGL will need to migrate to the updated wallet adapter system, which now offers enhanced support for multiple transactions.

New dependencies: None

[GabrielePicco]

Thanks for the contribution @owais-star! I left some questions and comments in the review

[GabrielePicco]

Thanks! LGTM